Digital etching of III‐V semiconductors with a monolayer precision induced by electropositive and 

electronegative atoms 

O.E. Tereshchenko, V.L. Alperovich, K.V. Toropetsky

Institute of Semiconductor Physics and Novosibirsk State University 

Russian Federation 

S. V. Eremeev, S. E. Kulkova

bInstitute of Strength Physics and Materials Science and  Tomsk State University, Russian Federation

Motivation: To develop the method of self‐limited etching of solidsurfaces with atomic layer precision.

Atomic layer depositionMolecular beam epitaxy

Layer by layer growth

(controlled by surface reconstructions)

Growth Etching

Layer by layer etching

Reactive ion etching:(plasma)

dry etching(gas etching)

intermixing, stoichiometric modification, surface roughening

It is difficult to control the etch depth precisely through the reactive ion etching due to the

fluctuation of the etch process

Cl (F) –diffuses into III-V and forms III-Clx (III-Fx)

Self-limited etching

How to apply self-limited etching for III-V?

As

Ga

Sb

InPreparation of reconstructed

III-V surfaces without V-fluxes1.

Adsorbate-induced selective interaction with the group III and V atoms2.

Structure and stoichiometryof GaAs(001) surface

As/GaAs(001):As/GaAs(001):HClHCl--iPAiPA--treatmenttreatment

(1x1) (2x4)/c(2x8) (4x2)/c(8x2)(3x6)/(2x6)

HCl-treatment

iPA

Temperature ( C)

3dA

s/3dG

a (a

rb. u

n.)

o200 300 400 500 600

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4(1x1)

c(2x8)

(4x6)

(2x6)(3x6)

/

c(8x2)As/Ga ratio on GaAs(001)after chemical treatment inHCl-iPA и subsequentannealing in UHV

(4x6)

480 °С 550 °С 580 °С

∆T ∼ 100°

420 °С

LowEnergyElectronDiffraction

Is it possible to reduce the transition temperature from As- to Ga-rich?

[001]

How the reversible transition between the Ga-rich and As-rich surfaces

at low temperature can be realized?

Questions we tried to answer:

O.E. Tereshchenko et al., JVST A17 (1999) 26551. Irreversible transition

2. Thermal defects generation

Idea: the self-limited etchingcontrolled by surface reconstructionsSURFACE REACTION CONTROL

(001) III-Velectronegative (filled dangling bonds)

As

Criterions for adsorbates:non-intermixing; selective interaction

with the substrate atoms

electropositive (empty dangling bonds)Surface stabilizationGa

?

Adsorbate-induced charge transfer: weakening of the backbonds

For polar faces of III-V: searching for adsorbates which selectively react with the elements of III and V groups

As-rich

Cs

Ga-rich

I - iodine

GaAs(001):

Goal: to  reveal the mechanism  providing  the s elec tive interac tion  of I andC s  with  Ga and  As  on  the GaAs (001) s urfac e and  to  us e this  s elec tivity to  implement the revers ible recons truc tion  trans itions  on  this  s urfac e.

Electronegativity concept

W.K. Wang et al. PRB, 61 (2000) 2164K.N. Eltsov et al. Proc. Int. Conf. Scanning Probe Microscopy (SPM-2002), March 2-6, 2002, Nizhny Novgorod, Russia, p.99.

I2/GaAs, InAs :

Cs/GaAs : O.E. Tereshchenko et al. PRB, 69 (2004) 125332

Experimental setup: electron spectrometer ADES-500 with nitrogen box for chemical treatment

Solid state electrochemical iodine source

Advantages of the electrochemical source:

Directed flow of iodine on a sample allows to avoid contamination of vacuum chamber

It is possible to calculate number of iodine molecule generated by the iodine source using ion current through the sourceExperimental procedures:

Preparation of clean As-rich and Ga-rich GaAs(001) surfaces by removing oxides in HCl-iPA solution with subsequent annealing in ultra-high vacuum

Cesium and iodine adsorption on GaAs(001) surface with subsequent annealing

Investigation of structural and electronic properties of GaAs(001) surface using LEED, XPS and photoemission

As-rich (2x4)/c(2x8)

Ga-rich (4x2)/c(8x2)

Kinetics of Cs and I adsorption on GaAs(001)

• Langmuir adsorption model with constant sticking coefficient.

• The sticking coefficients for As- и Ga-rich surfaces of GaAscoincide to within 5%.

0.0

0.4

0.5

0.8

1.2

1.6

2.01.0

Cesium deposition time (min)

Cs3

nten

sity

i

n

d (a

rb. u

).

Cs c

over

age

(ML

)

- As-stabilized

Photocurrentmax.

- Ga-stabilized

0 20 40 60 80 1000.0

Cs /GaAs(001) I /GaAs(001)

ICs

The difference in Cs adsorption on As-and Ga-rich surfaces is due to the difference in the interaction mechanism of Cs with arsenic and gallium surface atoms!

Cs/GaAs(001)

Wor

k fu

nctio

n ch

ange

s(eV

)

Cesium coverage (ML)0.0 0.2 0.4 0.6 0.8 1.0

I3nt

ensit

y (a

rb. u

)

i

n.d

- As-stabilized

- Ga-stabilized

8 106420Iodine deposition time (min)

0

765432

1

+- +

-

Work function variation  of GaAs(001) under Cs and I deposition

non-intermixing; selective interaction

Cs deposition on As and Ga – rich GaAs(001)

LEED:

CsAs-(2x4) Ga-(4x2)

0.5 ML Cs(1x1) (4x1)

Ga-(4x2)T=450oC

As-(2x4) Ga-(4x2)

(1x1) (4x1)

0.5 ML Cs550 °С

T=450oC

Ga-(4x2)Ga-(4x2)Ga-(4x2)

I2 deposition on As and Ga – rich GaAs(001)

LEED:

Ga-(4x2) I2As-(2x4)

As-(2x4) Ga-(4x2)0.5 ML I2

(1x1)/(2x1)(1x1)/(2x1) 0.5 ML I2

(1x1)/(2x1)(1x1)/(2x1)

As-(2x4)T=400oC T=450oC

As-(2x4)

As-(2x4)As-(2x4)

Cs ‐ induced low temperature 

(2х4) → (4х2) transition

Iodine ‐ induced(4х2) → (2х4) transition

0.5 ML Cs

(2x4)/c(2x8) (4x2)/c(8x2)

450°C

560°C

Alternative method of preparation of Ga- rich (4х2) surface at reduced temperature.

TAs-rich (2x4)

Iodine

T=400oC

Selective interaction of Cs and I with As and Ga – rich GaAs(001) surfaces

Cs

As-(2x4)Ga-(4x2)

(1x1)(4x1)

T=450oC

0.5 ML Cs

Ga-(4x2)Ga-(4x2)

As-(2x4)Ga-(4x2)

I2

0.5 ML I2

(1x1)/(2x1)(1x1)/(2x1)

T=400oC

As-(2x4)As-(2x4)

removal of 1 ML

Ga-rich As-rich

Layer‐by‐layer etching of GaAs(001)

0.00.10.20.30.40.50.60.70.8

321

(2x4)0.9 ML I 2

(2x4)

Number of (Cs, I ) cycle2

(4x2)

Cs+4 0 C5 o

(2x4)0.5 ML I 2

(4x2)Cs+4 0 C5 o

(2x4)0.25 ML I 2

4 0+ 0 oC 4 0+ 0 oC 4 0+ 0 oC

(4x2)Cs+4 0 C5 o

LEE

D sp

ot in

tens

ity

Quality of GaAs(001) surface during adsorption and desorption of cesium and

iodine

Photoemission experiment  Core-levels and surfacechemical shifts

sample

Cs (I)‐induced charge redistribution:photoemission measurements

Cs I2

73 75 7 77 9 73 75 7 77 9

50 51 52 53 54 55 56

72 73 74 75 76 77 78

50 51 52 53 54 55 56 5

72 73 74 75 76 77 78

As-(2x4)Ga-(4x2) As-(2x4)Ga-(4x2)

As 3d As 3d

Ga 3d Ga 3d

Kinetic energy, eV Kinetic energy, eV

1.0 1.5 2.0 2.5 3.0-0.1

0.0

0.1

0.2

0.3

0.4

0.5

∆ρ,

el.

R, Ang

Cs Ga(2a) Ga(2b) As(1)

Cs-D/As-rich_β2

∆ρ>0 ∆ρ<0∆ρ>0 ∆ρ<0D T2’

β2

T1

H3

D3

1.0 1.5 2.0 2.5 3.0-0.3-0.2-0.10.00.10.20.3

Cs Ga As

∆ρ, e

l.

R, A

As-richT2'

Cs on β2-GaAs(001)-(2x4): DFT

Charge integration at D position

)()()()( / rrrr GaAsIIGaAs ρρρρ −+=∆

I on GaAs(001): first principal calculation

)()()()( / rrrr GaAsIIGaAs ρρρρ −+=∆

β2-GaAs(001)-(2x4)

∆ρ<0∆ρ>0

ζ-GaAs(001)-(4x2)T4

∆ρ>0 ∆ρ<0S1

+-

Unpinned behavior of Fermi level at Cs/GaAs(001) 

0.2

0.4

0.6

20 400 500 600Temperature (°C )

ϕ s (

eV)

- Cs/As rich- without Cs

CsCs--induced surface states induced surface states passivationpassivation and unpinned and unpinned behavior behavior of the Fermi levelof the Fermi level

Summary

• The selective interaction of the iodine and cesium atoms with the GaAs(001) surface leads to a decrease in the bond energy of the Gaand As surface atoms, respectively, owing to the redistribution of the electron density in the near-surface region under the effect of electronegative and electropositive adsorbates.

• This selective interaction makes it possible to remove alternately the Gaand As monolayers in the iodine and cesium adsorption followed by heating at T ≤ 450°C and, thus, to implement reversible low-temperature transitions between the Ga- and As-stabilized reconstructions, as well as the atomic layer etching of the semiconductor with the physically ultimate monolayer accuracy.