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Surface conductivity of InSb (110) surface during oxygen adsorption
Volume 47A, number 5
PHYSICS LETTERS
22 April 1974
S U R F A C E C O N D U C T I V I T Y O F I n S b (1 10) S U R F A C E DURING
OXYGEN ADSORPTION
E.W. KREUTZ, E. RICKUS and N. SOTNIK L Physikalisches Institut, Technische Hochschule Darmstadt, Darmstadt, Germany Fed. Rep.
Received 15 March 1974 The surface conductivity of InSb (110) surfaces cleaned by the ion bombardment annealing technique was measured during oxygen adsorption. The surface conductivity of p-type InSb increases with coverage. The structural and electrical properties of semiconductor surfaces have been studied by numerous investigators [e.g. 1 - 5 ] . Herewith the surface properties of Ge and Si [ 1-3] have received much more attention than those of the I I I - V - compounds [4, 5]. In order to get detailed information on the electrical properties the surface conductivity of the InSb (110) surface which was cleaned by the ion bombardment annealing technique [6, 7] has been measured. Oxygen adsorption was used to influence the electronic band structure of the surface as was established by measurements of changes in surface conductivity. The investigations were performed in an all- metal ultrahigh vacuum system. The InSb specimens were cut from M.C.P. Ltd., Alperton Wembley, Middlesex, single crystal material having excess hole concentrations of about 5 X 1014 cm - 3 . The large sample faces were oriented to within 1 degree of (110) planes by the Laue X-ray backscattering method. Mechanical grinding, chemical polishing, contact fabricating, sample dimensions and experimental arrangement are described elsewhere [8]. Ar+ ion bombardment (current densities of 0.5 to 1.0/aA c m - 2 ; periods of 60 to 120 min; ion energies of 250 to 300 eV) in combination with annealing (annealing temperature of 400 to 420°C; periods of 30 to 120 rain) were used for the cleaning process. Oxygen adsorption was performed by stepwise raising of pressure and holding the samples for 5 minutes at a certain pressure. The real surface of p-type lnSb exhibits accumulation layers [9, 10] after etching in CP4A [11]. Consequently the cleaned surface is shunted by the other
real surfaces of the samples. To ensure that one is dealing during oxygen adsorption with surface conductivity changes of the cleaned surface, uncleaned crystals are submitted to oxygen. The overall conductivity of these crystals is not altered within the experimental errors during the control runs in the investigated pressure range. In the pressure range where the changes in surface conductivity of the cleaned InSb surface 0.4~T =95K
/
/
0.2.
/ ~o
o
~"
./
J
,o"
~"
,o"
~
Oxygen exposure (torr mini
Fig. 1. Change in surface conductance of the lnSb (110) surface of a p-type sample (excess hole concentration 4 × 1014 cm-3; length 11 mm, width 6 ram, thickness 0.7 mm) versus oxygen coverage.The data have been taken by increasing stepwise pressure. Aeo denotes the surface conductance after ion bombardment and annealing. 363
Volume 47A,'number 5
PHYSICS LETTERS
occur the surface conductivity of the real InSb surface is altered only at higher exposure times of several days. Fig. 1 shows the change o f surface conductivity as measured at T = 95 K versus oxygen coverage. Up to an exposure of 1 0 - 7 tort rain no changes in surface conductivity have been observed. Starting from the surface conductivity, measured immediately after ion b o m b a r d m e n t annealing, the surface conductivity then increases with oxygen coverage. At exposures of about 1 0 - 4 torr rain the change in surface conductivity saturates (fig. 1). Simultaneously the relative intensity of normal spots in the LEED pattern [8] decreases indicating a correlation of crystallographic and electronic structure o f the ion b o m b a r d e d and annealed InSb (110) surface. These observations coincide with the findings of other authors [12] that the intensity of ordinary spots decreases during oxygen adsorption on InSb ( 1 0 0 ) - , ( 1 1 1 ) - , and (111-) surfaces. Starting from the real surface the overall conductivity decreases during ion b o m b a r d m e n t [13] as well as the surface conductivity increases with oxygen coverage without passing a minimum. Consequently the ion bombarded and annealed InSb (110) surface should be p-type. ~fhese results are in general agreeinent with measurements o f photoemission on n-type lnSb with cleaved (110) surfaces [ 14] showing strongly p-type conduction.
364
22 April 1974
The authors should like to thank Prof. Dr. W. Waidelich for his keen interest in the present work. The authors are most grateful to the Deutsche Forschungsgemeinschaft for financial support.
References [ 1] A. Many, Y. Goldstein and N.B. Grover, Semiconductor surfaces (North Holland Publ. Co., Amsterdam 1965). [ 21 D.R. Frankl, Electrical properties of semiconductor surfaces (Pergamon Press, Oxford 1967). [ 3] W. MSnch, FestkSrperprobleme 13 (1973) 241. [4] J.tt. Dinan, L.K. Galbraith and T.E. Fischer, Surf. Sci. 26 (1971) 587. [51 P.E. Viljoen, M.S. Jazzar and T.E. Fischer, Surf. Sci. 32 (1972) 506. [6] D. Haneman, J. Phys. Chem. Solids 14 (1960) 162. [7] A.U. Mac Rae and G.W. Gobeli, J. Appl. Phys. 35 (1964) 1629. [8] To be published. [9] H. Huff, S. Kawaji and H.C. Gatos, Surf. Sci. 5 (1966) 399. [10] E.W. Kreutz, H. Pagnia and W. Waidelich, Phys. Stat. Sol. 27 (1968) K i l l . [ 11 ] A.F. Bogenschiitz, Atzpraxis fiir Halbleiter (C. ttanser Verlag, Mfinchen 1967). 112] D. Haneman, Phys. Rev. 12l (1961) 1093. [13] E. Richus, diploma work, TH Darmstadt 1974. [14] G.W. Gobeli and F.G. Allen, Phys. Rev. 137 (1965) 245.
PHYSICS LETTERS
22 April 1974
S U R F A C E C O N D U C T I V I T Y O F I n S b (1 10) S U R F A C E DURING
OXYGEN ADSORPTION
E.W. KREUTZ, E. RICKUS and N. SOTNIK L Physikalisches Institut, Technische Hochschule Darmstadt, Darmstadt, Germany Fed. Rep.
Received 15 March 1974 The surface conductivity of InSb (110) surfaces cleaned by the ion bombardment annealing technique was measured during oxygen adsorption. The surface conductivity of p-type InSb increases with coverage. The structural and electrical properties of semiconductor surfaces have been studied by numerous investigators [e.g. 1 - 5 ] . Herewith the surface properties of Ge and Si [ 1-3] have received much more attention than those of the I I I - V - compounds [4, 5]. In order to get detailed information on the electrical properties the surface conductivity of the InSb (110) surface which was cleaned by the ion bombardment annealing technique [6, 7] has been measured. Oxygen adsorption was used to influence the electronic band structure of the surface as was established by measurements of changes in surface conductivity. The investigations were performed in an all- metal ultrahigh vacuum system. The InSb specimens were cut from M.C.P. Ltd., Alperton Wembley, Middlesex, single crystal material having excess hole concentrations of about 5 X 1014 cm - 3 . The large sample faces were oriented to within 1 degree of (110) planes by the Laue X-ray backscattering method. Mechanical grinding, chemical polishing, contact fabricating, sample dimensions and experimental arrangement are described elsewhere [8]. Ar+ ion bombardment (current densities of 0.5 to 1.0/aA c m - 2 ; periods of 60 to 120 min; ion energies of 250 to 300 eV) in combination with annealing (annealing temperature of 400 to 420°C; periods of 30 to 120 rain) were used for the cleaning process. Oxygen adsorption was performed by stepwise raising of pressure and holding the samples for 5 minutes at a certain pressure. The real surface of p-type lnSb exhibits accumulation layers [9, 10] after etching in CP4A [11]. Consequently the cleaned surface is shunted by the other
real surfaces of the samples. To ensure that one is dealing during oxygen adsorption with surface conductivity changes of the cleaned surface, uncleaned crystals are submitted to oxygen. The overall conductivity of these crystals is not altered within the experimental errors during the control runs in the investigated pressure range. In the pressure range where the changes in surface conductivity of the cleaned InSb surface 0.4~T =95K
/
/
0.2.
/ ~o
o
~"
./
J
,o"
~"
,o"
~
Oxygen exposure (torr mini
Fig. 1. Change in surface conductance of the lnSb (110) surface of a p-type sample (excess hole concentration 4 × 1014 cm-3; length 11 mm, width 6 ram, thickness 0.7 mm) versus oxygen coverage.The data have been taken by increasing stepwise pressure. Aeo denotes the surface conductance after ion bombardment and annealing. 363
Volume 47A,'number 5
PHYSICS LETTERS
occur the surface conductivity of the real InSb surface is altered only at higher exposure times of several days. Fig. 1 shows the change o f surface conductivity as measured at T = 95 K versus oxygen coverage. Up to an exposure of 1 0 - 7 tort rain no changes in surface conductivity have been observed. Starting from the surface conductivity, measured immediately after ion b o m b a r d m e n t annealing, the surface conductivity then increases with oxygen coverage. At exposures of about 1 0 - 4 torr rain the change in surface conductivity saturates (fig. 1). Simultaneously the relative intensity of normal spots in the LEED pattern [8] decreases indicating a correlation of crystallographic and electronic structure o f the ion b o m b a r d e d and annealed InSb (110) surface. These observations coincide with the findings of other authors [12] that the intensity of ordinary spots decreases during oxygen adsorption on InSb ( 1 0 0 ) - , ( 1 1 1 ) - , and (111-) surfaces. Starting from the real surface the overall conductivity decreases during ion b o m b a r d m e n t [13] as well as the surface conductivity increases with oxygen coverage without passing a minimum. Consequently the ion bombarded and annealed InSb (110) surface should be p-type. ~fhese results are in general agreeinent with measurements o f photoemission on n-type lnSb with cleaved (110) surfaces [ 14] showing strongly p-type conduction.
364
22 April 1974
The authors should like to thank Prof. Dr. W. Waidelich for his keen interest in the present work. The authors are most grateful to the Deutsche Forschungsgemeinschaft for financial support.
References [ 1] A. Many, Y. Goldstein and N.B. Grover, Semiconductor surfaces (North Holland Publ. Co., Amsterdam 1965). [ 21 D.R. Frankl, Electrical properties of semiconductor surfaces (Pergamon Press, Oxford 1967). [ 3] W. MSnch, FestkSrperprobleme 13 (1973) 241. [4] J.tt. Dinan, L.K. Galbraith and T.E. Fischer, Surf. Sci. 26 (1971) 587. [51 P.E. Viljoen, M.S. Jazzar and T.E. Fischer, Surf. Sci. 32 (1972) 506. [6] D. Haneman, J. Phys. Chem. Solids 14 (1960) 162. [7] A.U. Mac Rae and G.W. Gobeli, J. Appl. Phys. 35 (1964) 1629. [8] To be published. [9] H. Huff, S. Kawaji and H.C. Gatos, Surf. Sci. 5 (1966) 399. [10] E.W. Kreutz, H. Pagnia and W. Waidelich, Phys. Stat. Sol. 27 (1968) K i l l . [ 11 ] A.F. Bogenschiitz, Atzpraxis fiir Halbleiter (C. ttanser Verlag, Mfinchen 1967). 112] D. Haneman, Phys. Rev. 12l (1961) 1093. [13] E. Richus, diploma work, TH Darmstadt 1974. [14] G.W. Gobeli and F.G. Allen, Phys. Rev. 137 (1965) 245.