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Copyright copy 2011 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 11 10949ndash10953 2011

Enhanced Wet Etching of PatternedGaN with Ion Implantation

Yuan Gao13 Chune Lan1 Jianming Xue1 Sha Yan1 Yugang Wang1lowastFujun Xu2 Bo Shen2 and Paul K Chu3

1State Key Laboratory of Nuclear Physics and Technology Peking UniversityBeijing 100871 Peoplersquos Republic of China

2State Key Laboratory for Artificial Microstructures and Mesoscopic PhysicsPeking University Beijing 100871 Peoplersquos Republic of China

3Department of Physics and Materials Science City University of Hong Kong83 Tat Chee Avenue Kowloon 999077 Hong Kong

We present the enhanced wet etching of GaN epilayer implanted with Au+ ion Patterned GaN with2 m-wide sink-like strips was achieved by using 500 keV Au+ ion implantation and KOH etchingThe Dependence of etching depth on etching time for the implantation at different ion fluences wasinvestigated The experiment showed that the damaged GaN area could be almost etched out athigh ion fluence and the etching depth could exceed the project range of incident 500 keV Au+ ionThe etch pits could be observed at the bottom of the etched area The sim400 nm depth etching couldbe achieved with high fluence implantation after a long etching time and the edge of etched areacould remain clear until the etching process had passed 40 min As-deposited SiO2 spheres wereused to mask the GaN sample in implantation process to investigate the etching effect sim70 nmwave of the GaN surface was observed The results of our experiments may suggest an approachto the fabricating of GaN devices

Keywords GaN Implantation Wet Etching KOH

1 INTRODUCTION

Gallium nitride (GaN) is a wide-band gap semiconduc-tor material with high thermal conductivity high meltingpoint and a high degree of hardness The outstandingphysical and chemical properties of GaN make it a suitablematerial in advanced optoelectronic and microelectronicdevice applications eg light-emitting devices laserdiodes and ultraviolet detectors1 Various dry etchantshave been investigated on GaN for its excellent chemi-cal stability as characterized by its invulnerabilities suchas electron cyclotron resonance (ECR) inductively cou-pled plasmas (ICP) reactive ion etching (RIE) and pho-toassisted dry etching2ndash4 Nevertheless there are severaldisadvantages to dry etching including ion- induced dam-age and difficulty in obtaining smooth sidewalls56 Wetetching has the advantage for providing low equipmentcost and complexity low surface damage and selective-ness of different materials As an important complement

lowastAuthor to whom correspondence should be addressed

to dry etching wet etching has a variety of applications towide band gap semiconductor technology including defectdecoration polarity and polytypic identification by pro-ducing characteristic pits or hillocks and device fabrica-tion on smooth surfaces7 However only very low etchrates have been reported for GaN films using wet chemicaletchants89 In this paper we have developed the enhancedwet etching with ion implantation on the GaN surfacewith photoresist or SiO2 spheres patterned The Depen-dence of etching depth on etching time at different ionfluences was investigated The experiment showed that thedamaged GaN area induced by ion implantation could bealmost etched out by KOH solution and the etching depthcould exceed the project range of incident 500 keV Au+

ion Moreover As-deposited SiO2 spheres were used tomask the GaN sample in implantation process to investi-gate the etching effect sim70 nm wave of the GaN surfacewas observed The results of our experiments may suggestan approach to the fabricating of GaN micro and nanodevices

J Nanosci Nanotechnol 2011 Vol 11 No 12 1533-488020111110949005 doi101166jnn20114055 10949

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Enhanced Wet Etching of Patterned GaN with Ion Implantation Gao et al

2 EXPERIMENTAL DETAILS

A sim2 m-thick wurtzite undoped GaN (0001) epilayerused in this research program were epitaxially grown ona c-plane sapphire substrate by metal-organic chemicalvapor deposition (MOCVD) The mass density of theGaN layer is about 61 gcm3 Implantation of 500 keVAu+ ions was performed by using a 2times 17 MV tan-dem accelerator (NEC 5SDH-2) at room temperature(RT) with ion fluence from 5times 1014 to 3times 1016 cmminus2The implantations were carried out at a constant beamflux of 25 times 1013 cmminus2 middot sminus1 During implantation toavoid channeling effect the sample crystallographic axes(0001) were titled by sim7 relative to the incident ionbeam As shown in Figure 1 before implantation someGaN samples were masked by a 2 m-thick photore-sist (AZ 6130) patterned with 2 m-wide strips and5 m-wide spacing and were removed after implantation

Fig 1 Schematic diagram of the fabricating process of the patternedGaN

by organic solvent (Acetone) The other virgin GaNsamples were masked with as-deposited SiO2 spheres(d = 340 nm) in implantation The implanted GaN sam-ples were wet etched for 20ndash120 min in 2 mol middotLminus1 KOHat 80 C The surface morphology of the implanted andetched GaN was studied with contact-mode atomic forcemicroscopy (AFM SPA400 SPI3800N) and scanning elec-tron microscopy (SEM STARTA DB235) Because theunimplanted area of GaN samples is hardly etched byKOH solution the etch depth could be considered to beequal to the step height between implanted and unim-planted area measured with AFM

3 RESULTS AND DISCUSSION

Figure 2 shows the dependence of etching depth on etch-ing time for the implantation at three different ion fluen-cies 5times1014 5times1015 and 3times1016 cmminus2 Before etchingThe sim40 nm swelling and sim200 nm depth erosion on pat-terned GaN surface after being implanted at the fluence of5times 1015 cmminus2 and 3times 1016 cmminus2 have been investigatedrespectively (The step height has been marked at axes0 minute as shown in Fig 2) The details about swellingor erosion will be shown in another article10

The evolution of etch rate could be divided into threestages At the first 20 min etching there was a negligi-bly small etch rate of GaN implanted at the fluence of5times1014 cmminus2 The average etch rate of GaN implanted atthe fluence of 5times1015 and 3times1016 cmminus2 was sim8 nmminwhich was higher than the rate (lt1 nmmin in 50 KOHsolution at 83 C) mentioned in Ref [11] After etchedfor 20 min there was an increase of etch rate of GaNimplanted at the fluence of 5times 1014 cmminus2 but still keptless than 2 nmmin There was only 20 nm increase ofetching depth in GaN implanted at the fluence of 5times1015

and 3times1016 cmminus2 After etched for 80 min the roughnessof etched GaN sidewalls increased to a high point and the

Fig 2 Dependence of etching depth on etching time for the implanta-tion of 500 keV Au+ ions at different ion fluences

10950 J Nanosci Nanotechnol 11 10949ndash10953 2011

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Gao et al Enhanced Wet Etching of Patterned GaN with Ion Implantation

(a) (b)

Fig 3 AFM image with cross sectional profile (a) and SEM image (b) of the GaN sample surface implanted through the mask with 500 keV Au+

at RT to the ion fluence of 5times1015 cmminus2 and etched for 20 min in 2 mol middotLminus1 KOH at 80 C

etching pattern was distorted which made the increase ofetching depth no senseFigure 3 shows the surface morphology and section

of the GaN wet etched for 20 min in KOH at 80 Cafter being implanted with 500 keV Au+ at fluence of5times1015 cmminus2 The smooth unimplanted surface and theetched implantaed area could been observed in the AFMand SEM micrograph of Figure 3 Microscopy imagesshow that the damaged area where the anomalous swellingmentioned above was observed had been taken off byapplying wet etching approach The etching depth is

Fig 4 SEM image of the patterned GaN sample implanted through themask with 500 keV Au+ at RT to the ion fluence of 5times1015 cmminus2 andetched for 40 min in 2 mol middotLminus1 KOH at 80 C

sim130 nm and the 2 m-wide strip of the implantedarea comparatively maintained its original width The stripsidewall was vertical and smooth indicating the useful-ness of this etching approach in device fabrication It isinteresting to note that the etching depth has exceededthe peak projected range of incident 500 keV Au+ ion(sim70 nm stimulated based on SRIM200612 Consideredwith the threshold displacement energy for both Ga andN is 25 eV1 at the etched bottom corresponding with theprojected range 130 nm the average number of Ga and

Fig 5 SEM image of the patterned GaN sample implanted through themask with 500 keV Au+ at RT to the ion fluence of 3times1016 cmminus2 andetched for 40 min in 2 mol middotLminus1 KOH at 80 C

J Nanosci Nanotechnol 11 10949ndash10953 2011 10951

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ARTIC

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Enhanced Wet Etching of Patterned GaN with Ion Implantation Gao et al

N vacancies induced by one Au+ ion is 025 and the lat-tice damage induced by ion implantation at the fluence of5times1015 cmminus2 is sim3 dpa (3 displacement per atom stim-ulated based on SRIM2006) The result maybe suggestedthe threshold of lattice damage at which level the enhancedetching by ion implantation could be achievedThe etch pits were obvious at the bottom of the sink-

like strip with a very low density (about 107 cmminus2 asshown in Figure 3(b) and the detail of pit was observed inthe GaN sample etched for 40 min as shown in Figure 4The etch pits exhibited hexagon composed by 6 compet-ing etch planes with intersecting the c plane suggestingthe sites having original defects which etched by KOHsolution associated with the ion implantation damage asmentioned in Ref [13] Figure 5 shows the surface mor-phology of GaN wet etched for 40 min in KOH at 80 Cafter being implanted with 500 keV Au+ at the fluence of3times 1016 cmminus2 The etching depth is sim400 nm including

(a)

(b)

Fig 6 (a) Schematic diagram of as-deposited SiO2 spheres maskedGaN and (b) the AFM image with cross sectional profile of the GaNepilayer implanted through the spheres mask with 500 keV Au+at RT tothefluence of 5times 1015 cmminus2 after wet etched for 20 min in 2 mol middotLminus1

KOH at 80 C

the ion erosion depth It is obvious that the width of theimplanted area increased after etching and the sidewallwas eroded heavily by KOH solution The density of etchpits at strip bottom increased to 108 cmminus2 which may beattributed to the damage induced by higher ion implanta-tion fluenceAs-deposited SiO2 spheres (d = 340 nm) were also

used to mask the GaN sample in implantation process toinvestigate the etching effect The SiO2 spheres had beenremoved before GaN was etched The sim70 nm wave ofthe GaN surface was observed after being implanted with500 keV Au+ at RT to the fluence of 5times1015 cmminus2 and wetetched for 20 min in 2 mol middotLminus1 KOH at 80 C as shownin Figure 6 The results suggest an approach to makingmicro or even nano-level structures and the patterned localdoping or electrical isolation may also be tried which isunder investigation in our project

4 CONCLUSIONS

An enhanced wet etching process of GaN epilayer hasbeen developed by ion implantation approach The depen-dence of etching depth on etching time for the implantationat different ion fluences was investigated The averageetch rate of GaN implanted at the fluence of 5times 1015

and 3times1016 cmminus2 was sim8 nmmin in 2 mol middotLminus1 KOHat 80 C at the first 20 min AFM and SEM analysis ofthe etched area indicated the usefulness of this etchingapproach in device fabrication when the ion influence was5times1015 cmminus2 The etch pits were observed at the bottomof the sink-like strip and the threshold of lattice damageat which level the enhanced etching by ion implantationcould be achieved was suggested to be 3 dpa The SiO2

spheres mask was also used to investigate an approach toproduce nano-level structures

Acknowledgments This work is financially supportedby the Ministry of Science and Technology of China(2008CB717803 2010CB832904) and the FundamentalResearch Funds for the Central Universities

References and Notes

1 W Jiang W J Weber C M Wang K M Wang and K Sun DefectDiffus Forum 226ndash228 91 (2004)

2 R T Leonard and S M Bedair Appl Phys Lett 68 794 (1996)3 A Szczesny P Sniecikowski J Szmidt and A Werbowy Vacuum

70 249 (2003)4 R J Shul G B McClellan S J Pearton C R Abernathy

C Constantine and C Barratt Electronics Lett 32 1408(1996)

5 F Ren J R Lothian S J Pearton C R Abernahty C B VartuliJ D Mackenzie R G Wilson and R F Karlicek J ElectronMater 26 1287 (1997)

6 K H Baik and S J Pearton Appl Surf Sci 255 5948(2009)

7 D Zhuang and J H Edgar Mater Sci Eng R 48 1 (2005)

10952 J Nanosci Nanotechnol 11 10949ndash10953 2011

RESEARCH

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Enhanced Wet Etching of Patterned GaN with Ion Implantation Gao et al

2 EXPERIMENTAL DETAILS

A sim2 m-thick wurtzite undoped GaN (0001) epilayerused in this research program were epitaxially grown ona c-plane sapphire substrate by metal-organic chemicalvapor deposition (MOCVD) The mass density of theGaN layer is about 61 gcm3 Implantation of 500 keVAu+ ions was performed by using a 2times 17 MV tan-dem accelerator (NEC 5SDH-2) at room temperature(RT) with ion fluence from 5times 1014 to 3times 1016 cmminus2The implantations were carried out at a constant beamflux of 25 times 1013 cmminus2 middot sminus1 During implantation toavoid channeling effect the sample crystallographic axes(0001) were titled by sim7 relative to the incident ionbeam As shown in Figure 1 before implantation someGaN samples were masked by a 2 m-thick photore-sist (AZ 6130) patterned with 2 m-wide strips and5 m-wide spacing and were removed after implantation

Fig 1 Schematic diagram of the fabricating process of the patternedGaN

by organic solvent (Acetone) The other virgin GaNsamples were masked with as-deposited SiO2 spheres(d = 340 nm) in implantation The implanted GaN sam-ples were wet etched for 20ndash120 min in 2 mol middotLminus1 KOHat 80 C The surface morphology of the implanted andetched GaN was studied with contact-mode atomic forcemicroscopy (AFM SPA400 SPI3800N) and scanning elec-tron microscopy (SEM STARTA DB235) Because theunimplanted area of GaN samples is hardly etched byKOH solution the etch depth could be considered to beequal to the step height between implanted and unim-planted area measured with AFM

3 RESULTS AND DISCUSSION

Figure 2 shows the dependence of etching depth on etch-ing time for the implantation at three different ion fluen-cies 5times1014 5times1015 and 3times1016 cmminus2 Before etchingThe sim40 nm swelling and sim200 nm depth erosion on pat-terned GaN surface after being implanted at the fluence of5times 1015 cmminus2 and 3times 1016 cmminus2 have been investigatedrespectively (The step height has been marked at axes0 minute as shown in Fig 2) The details about swellingor erosion will be shown in another article10

The evolution of etch rate could be divided into threestages At the first 20 min etching there was a negligi-bly small etch rate of GaN implanted at the fluence of5times1014 cmminus2 The average etch rate of GaN implanted atthe fluence of 5times1015 and 3times1016 cmminus2 was sim8 nmminwhich was higher than the rate (lt1 nmmin in 50 KOHsolution at 83 C) mentioned in Ref [11] After etchedfor 20 min there was an increase of etch rate of GaNimplanted at the fluence of 5times 1014 cmminus2 but still keptless than 2 nmmin There was only 20 nm increase ofetching depth in GaN implanted at the fluence of 5times1015

and 3times1016 cmminus2 After etched for 80 min the roughnessof etched GaN sidewalls increased to a high point and the

Fig 2 Dependence of etching depth on etching time for the implanta-tion of 500 keV Au+ ions at different ion fluences

10950 J Nanosci Nanotechnol 11 10949ndash10953 2011

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Gao et al Enhanced Wet Etching of Patterned GaN with Ion Implantation

(a) (b)

Fig 3 AFM image with cross sectional profile (a) and SEM image (b) of the GaN sample surface implanted through the mask with 500 keV Au+

at RT to the ion fluence of 5times1015 cmminus2 and etched for 20 min in 2 mol middotLminus1 KOH at 80 C

etching pattern was distorted which made the increase ofetching depth no senseFigure 3 shows the surface morphology and section

of the GaN wet etched for 20 min in KOH at 80 Cafter being implanted with 500 keV Au+ at fluence of5times1015 cmminus2 The smooth unimplanted surface and theetched implantaed area could been observed in the AFMand SEM micrograph of Figure 3 Microscopy imagesshow that the damaged area where the anomalous swellingmentioned above was observed had been taken off byapplying wet etching approach The etching depth is

Fig 4 SEM image of the patterned GaN sample implanted through themask with 500 keV Au+ at RT to the ion fluence of 5times1015 cmminus2 andetched for 40 min in 2 mol middotLminus1 KOH at 80 C

sim130 nm and the 2 m-wide strip of the implantedarea comparatively maintained its original width The stripsidewall was vertical and smooth indicating the useful-ness of this etching approach in device fabrication It isinteresting to note that the etching depth has exceededthe peak projected range of incident 500 keV Au+ ion(sim70 nm stimulated based on SRIM200612 Consideredwith the threshold displacement energy for both Ga andN is 25 eV1 at the etched bottom corresponding with theprojected range 130 nm the average number of Ga and

Fig 5 SEM image of the patterned GaN sample implanted through themask with 500 keV Au+ at RT to the ion fluence of 3times1016 cmminus2 andetched for 40 min in 2 mol middotLminus1 KOH at 80 C

J Nanosci Nanotechnol 11 10949ndash10953 2011 10951

RESEARCH

ARTIC

LE

Enhanced Wet Etching of Patterned GaN with Ion Implantation Gao et al

N vacancies induced by one Au+ ion is 025 and the lat-tice damage induced by ion implantation at the fluence of5times1015 cmminus2 is sim3 dpa (3 displacement per atom stim-ulated based on SRIM2006) The result maybe suggestedthe threshold of lattice damage at which level the enhancedetching by ion implantation could be achievedThe etch pits were obvious at the bottom of the sink-

like strip with a very low density (about 107 cmminus2 asshown in Figure 3(b) and the detail of pit was observed inthe GaN sample etched for 40 min as shown in Figure 4The etch pits exhibited hexagon composed by 6 compet-ing etch planes with intersecting the c plane suggestingthe sites having original defects which etched by KOHsolution associated with the ion implantation damage asmentioned in Ref [13] Figure 5 shows the surface mor-phology of GaN wet etched for 40 min in KOH at 80 Cafter being implanted with 500 keV Au+ at the fluence of3times 1016 cmminus2 The etching depth is sim400 nm including

(a)

(b)

Fig 6 (a) Schematic diagram of as-deposited SiO2 spheres maskedGaN and (b) the AFM image with cross sectional profile of the GaNepilayer implanted through the spheres mask with 500 keV Au+at RT tothefluence of 5times 1015 cmminus2 after wet etched for 20 min in 2 mol middotLminus1

KOH at 80 C

the ion erosion depth It is obvious that the width of theimplanted area increased after etching and the sidewallwas eroded heavily by KOH solution The density of etchpits at strip bottom increased to 108 cmminus2 which may beattributed to the damage induced by higher ion implanta-tion fluenceAs-deposited SiO2 spheres (d = 340 nm) were also

used to mask the GaN sample in implantation process toinvestigate the etching effect The SiO2 spheres had beenremoved before GaN was etched The sim70 nm wave ofthe GaN surface was observed after being implanted with500 keV Au+ at RT to the fluence of 5times1015 cmminus2 and wetetched for 20 min in 2 mol middotLminus1 KOH at 80 C as shownin Figure 6 The results suggest an approach to makingmicro or even nano-level structures and the patterned localdoping or electrical isolation may also be tried which isunder investigation in our project

4 CONCLUSIONS

An enhanced wet etching process of GaN epilayer hasbeen developed by ion implantation approach The depen-dence of etching depth on etching time for the implantationat different ion fluences was investigated The averageetch rate of GaN implanted at the fluence of 5times 1015

and 3times1016 cmminus2 was sim8 nmmin in 2 mol middotLminus1 KOHat 80 C at the first 20 min AFM and SEM analysis ofthe etched area indicated the usefulness of this etchingapproach in device fabrication when the ion influence was5times1015 cmminus2 The etch pits were observed at the bottomof the sink-like strip and the threshold of lattice damageat which level the enhanced etching by ion implantationcould be achieved was suggested to be 3 dpa The SiO2

spheres mask was also used to investigate an approach toproduce nano-level structures

Acknowledgments This work is financially supportedby the Ministry of Science and Technology of China(2008CB717803 2010CB832904) and the FundamentalResearch Funds for the Central Universities

References and Notes

1 W Jiang W J Weber C M Wang K M Wang and K Sun DefectDiffus Forum 226ndash228 91 (2004)

2 R T Leonard and S M Bedair Appl Phys Lett 68 794 (1996)3 A Szczesny P Sniecikowski J Szmidt and A Werbowy Vacuum

70 249 (2003)4 R J Shul G B McClellan S J Pearton C R Abernathy

C Constantine and C Barratt Electronics Lett 32 1408(1996)

5 F Ren J R Lothian S J Pearton C R Abernahty C B VartuliJ D Mackenzie R G Wilson and R F Karlicek J ElectronMater 26 1287 (1997)

6 K H Baik and S J Pearton Appl Surf Sci 255 5948(2009)

7 D Zhuang and J H Edgar Mater Sci Eng R 48 1 (2005)

10952 J Nanosci Nanotechnol 11 10949ndash10953 2011

RESEARCH

ARTIC

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Gao et al Enhanced Wet Etching of Patterned GaN with Ion Implantation

(a) (b)

Fig 3 AFM image with cross sectional profile (a) and SEM image (b) of the GaN sample surface implanted through the mask with 500 keV Au+

at RT to the ion fluence of 5times1015 cmminus2 and etched for 20 min in 2 mol middotLminus1 KOH at 80 C

etching pattern was distorted which made the increase ofetching depth no senseFigure 3 shows the surface morphology and section

of the GaN wet etched for 20 min in KOH at 80 Cafter being implanted with 500 keV Au+ at fluence of5times1015 cmminus2 The smooth unimplanted surface and theetched implantaed area could been observed in the AFMand SEM micrograph of Figure 3 Microscopy imagesshow that the damaged area where the anomalous swellingmentioned above was observed had been taken off byapplying wet etching approach The etching depth is

Fig 4 SEM image of the patterned GaN sample implanted through themask with 500 keV Au+ at RT to the ion fluence of 5times1015 cmminus2 andetched for 40 min in 2 mol middotLminus1 KOH at 80 C

sim130 nm and the 2 m-wide strip of the implantedarea comparatively maintained its original width The stripsidewall was vertical and smooth indicating the useful-ness of this etching approach in device fabrication It isinteresting to note that the etching depth has exceededthe peak projected range of incident 500 keV Au+ ion(sim70 nm stimulated based on SRIM200612 Consideredwith the threshold displacement energy for both Ga andN is 25 eV1 at the etched bottom corresponding with theprojected range 130 nm the average number of Ga and

Fig 5 SEM image of the patterned GaN sample implanted through themask with 500 keV Au+ at RT to the ion fluence of 3times1016 cmminus2 andetched for 40 min in 2 mol middotLminus1 KOH at 80 C

J Nanosci Nanotechnol 11 10949ndash10953 2011 10951

RESEARCH

ARTIC

LE

Enhanced Wet Etching of Patterned GaN with Ion Implantation Gao et al

N vacancies induced by one Au+ ion is 025 and the lat-tice damage induced by ion implantation at the fluence of5times1015 cmminus2 is sim3 dpa (3 displacement per atom stim-ulated based on SRIM2006) The result maybe suggestedthe threshold of lattice damage at which level the enhancedetching by ion implantation could be achievedThe etch pits were obvious at the bottom of the sink-

like strip with a very low density (about 107 cmminus2 asshown in Figure 3(b) and the detail of pit was observed inthe GaN sample etched for 40 min as shown in Figure 4The etch pits exhibited hexagon composed by 6 compet-ing etch planes with intersecting the c plane suggestingthe sites having original defects which etched by KOHsolution associated with the ion implantation damage asmentioned in Ref [13] Figure 5 shows the surface mor-phology of GaN wet etched for 40 min in KOH at 80 Cafter being implanted with 500 keV Au+ at the fluence of3times 1016 cmminus2 The etching depth is sim400 nm including

(a)

(b)

Fig 6 (a) Schematic diagram of as-deposited SiO2 spheres maskedGaN and (b) the AFM image with cross sectional profile of the GaNepilayer implanted through the spheres mask with 500 keV Au+at RT tothefluence of 5times 1015 cmminus2 after wet etched for 20 min in 2 mol middotLminus1

KOH at 80 C

the ion erosion depth It is obvious that the width of theimplanted area increased after etching and the sidewallwas eroded heavily by KOH solution The density of etchpits at strip bottom increased to 108 cmminus2 which may beattributed to the damage induced by higher ion implanta-tion fluenceAs-deposited SiO2 spheres (d = 340 nm) were also

used to mask the GaN sample in implantation process toinvestigate the etching effect The SiO2 spheres had beenremoved before GaN was etched The sim70 nm wave ofthe GaN surface was observed after being implanted with500 keV Au+ at RT to the fluence of 5times1015 cmminus2 and wetetched for 20 min in 2 mol middotLminus1 KOH at 80 C as shownin Figure 6 The results suggest an approach to makingmicro or even nano-level structures and the patterned localdoping or electrical isolation may also be tried which isunder investigation in our project

4 CONCLUSIONS

An enhanced wet etching process of GaN epilayer hasbeen developed by ion implantation approach The depen-dence of etching depth on etching time for the implantationat different ion fluences was investigated The averageetch rate of GaN implanted at the fluence of 5times 1015

and 3times1016 cmminus2 was sim8 nmmin in 2 mol middotLminus1 KOHat 80 C at the first 20 min AFM and SEM analysis ofthe etched area indicated the usefulness of this etchingapproach in device fabrication when the ion influence was5times1015 cmminus2 The etch pits were observed at the bottomof the sink-like strip and the threshold of lattice damageat which level the enhanced etching by ion implantationcould be achieved was suggested to be 3 dpa The SiO2

spheres mask was also used to investigate an approach toproduce nano-level structures

Acknowledgments This work is financially supportedby the Ministry of Science and Technology of China(2008CB717803 2010CB832904) and the FundamentalResearch Funds for the Central Universities

References and Notes

1 W Jiang W J Weber C M Wang K M Wang and K Sun DefectDiffus Forum 226ndash228 91 (2004)

2 R T Leonard and S M Bedair Appl Phys Lett 68 794 (1996)3 A Szczesny P Sniecikowski J Szmidt and A Werbowy Vacuum

70 249 (2003)4 R J Shul G B McClellan S J Pearton C R Abernathy

C Constantine and C Barratt Electronics Lett 32 1408(1996)

5 F Ren J R Lothian S J Pearton C R Abernahty C B VartuliJ D Mackenzie R G Wilson and R F Karlicek J ElectronMater 26 1287 (1997)

6 K H Baik and S J Pearton Appl Surf Sci 255 5948(2009)

7 D Zhuang and J H Edgar Mater Sci Eng R 48 1 (2005)

10952 J Nanosci Nanotechnol 11 10949ndash10953 2011

RESEARCH

ARTIC

LE

Enhanced Wet Etching of Patterned GaN with Ion Implantation Gao et al

N vacancies induced by one Au+ ion is 025 and the lat-tice damage induced by ion implantation at the fluence of5times1015 cmminus2 is sim3 dpa (3 displacement per atom stim-ulated based on SRIM2006) The result maybe suggestedthe threshold of lattice damage at which level the enhancedetching by ion implantation could be achievedThe etch pits were obvious at the bottom of the sink-

like strip with a very low density (about 107 cmminus2 asshown in Figure 3(b) and the detail of pit was observed inthe GaN sample etched for 40 min as shown in Figure 4The etch pits exhibited hexagon composed by 6 compet-ing etch planes with intersecting the c plane suggestingthe sites having original defects which etched by KOHsolution associated with the ion implantation damage asmentioned in Ref [13] Figure 5 shows the surface mor-phology of GaN wet etched for 40 min in KOH at 80 Cafter being implanted with 500 keV Au+ at the fluence of3times 1016 cmminus2 The etching depth is sim400 nm including

(a)

(b)

Fig 6 (a) Schematic diagram of as-deposited SiO2 spheres maskedGaN and (b) the AFM image with cross sectional profile of the GaNepilayer implanted through the spheres mask with 500 keV Au+at RT tothefluence of 5times 1015 cmminus2 after wet etched for 20 min in 2 mol middotLminus1

KOH at 80 C

the ion erosion depth It is obvious that the width of theimplanted area increased after etching and the sidewallwas eroded heavily by KOH solution The density of etchpits at strip bottom increased to 108 cmminus2 which may beattributed to the damage induced by higher ion implanta-tion fluenceAs-deposited SiO2 spheres (d = 340 nm) were also

used to mask the GaN sample in implantation process toinvestigate the etching effect The SiO2 spheres had beenremoved before GaN was etched The sim70 nm wave ofthe GaN surface was observed after being implanted with500 keV Au+ at RT to the fluence of 5times1015 cmminus2 and wetetched for 20 min in 2 mol middotLminus1 KOH at 80 C as shownin Figure 6 The results suggest an approach to makingmicro or even nano-level structures and the patterned localdoping or electrical isolation may also be tried which isunder investigation in our project

4 CONCLUSIONS

An enhanced wet etching process of GaN epilayer hasbeen developed by ion implantation approach The depen-dence of etching depth on etching time for the implantationat different ion fluences was investigated The averageetch rate of GaN implanted at the fluence of 5times 1015

and 3times1016 cmminus2 was sim8 nmmin in 2 mol middotLminus1 KOHat 80 C at the first 20 min AFM and SEM analysis ofthe etched area indicated the usefulness of this etchingapproach in device fabrication when the ion influence was5times1015 cmminus2 The etch pits were observed at the bottomof the sink-like strip and the threshold of lattice damageat which level the enhanced etching by ion implantationcould be achieved was suggested to be 3 dpa The SiO2

spheres mask was also used to investigate an approach toproduce nano-level structures

Acknowledgments This work is financially supportedby the Ministry of Science and Technology of China(2008CB717803 2010CB832904) and the FundamentalResearch Funds for the Central Universities

References and Notes

1 W Jiang W J Weber C M Wang K M Wang and K Sun DefectDiffus Forum 226ndash228 91 (2004)

2 R T Leonard and S M Bedair Appl Phys Lett 68 794 (1996)3 A Szczesny P Sniecikowski J Szmidt and A Werbowy Vacuum

70 249 (2003)4 R J Shul G B McClellan S J Pearton C R Abernathy

C Constantine and C Barratt Electronics Lett 32 1408(1996)

5 F Ren J R Lothian S J Pearton C R Abernahty C B VartuliJ D Mackenzie R G Wilson and R F Karlicek J ElectronMater 26 1287 (1997)

6 K H Baik and S J Pearton Appl Surf Sci 255 5948(2009)

7 D Zhuang and J H Edgar Mater Sci Eng R 48 1 (2005)

10952 J Nanosci Nanotechnol 11 10949ndash10953 2011

RESEARCH

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LE

Gao et al Enhanced Wet Etching of Patterned GaN with Ion Implantation

8 S J Pearton C R Abernathy F Ren J R Lothian P W Wiskand A Katz J Vac Sci Technol A 11 1772 (1993)

9 J R Mileham S J Pearton C R Abernathy J D MacKenzieR J Shul and S P Kilcoyne J Vac Sci Technol A 14 836(1996)

10 Y Gao C Lan J Xue S Yan Y Wang F Xu B Shen andY Zhang Nucl Instr Meth Phys Res B 268 3207 (2010)

11 D A Stocker E F Schubert and J M Redwing Appl Phys Lett73 2654 (1998)

12 J F Ziegler J P Biearsack and U Littmark The Stop-ping and Range of Ions in Solids Pergamon Press New York(1985)

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Received 8 August 2010 RevisedAccepted 20 October 2010

J Nanosci Nanotechnol 11 10949ndash10953 2011 10953