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Calculations of the atomic geometries of the (110) surfaces of III–V compound semiconductors
A12 Surface Science 149 (1985) 341-348 North-Holland, Amsterdam DONOR-ACCEPTOR OXO III-V SEMICONDUCTORS Roger CHANG
341 BONDS
T O N, P, As A N D Sb S T A T E S
a n d W i l l i a m A. G O D D A R D
OF
III
Arthur Amos Noyes Laboratory of Chemical Physics *, California Institute of Technology, Pasadena, California 91125, USA Received 25 June 1984; accepted for publication 25 September 1984 As a model for a proposed phosphine oxide-type initial state in the oxidation of III-V semiconductors, we have examined the structure and bonding of the phosphine oxide-type bond in CI 3Y = O where Y = N, P, As, ans Sb. We calculate an Y = O bond energy of 114 kcal for P = O, in reasonable agreement with experiment, 123 kcal/mol. The other calculated bond energies (kcal/mol) are 47 (N), 82 (As), and 63 (Sb). Based on these results, we conclude that such bonds should play an important role in phosphides and are likely to be important in arsenides but not in nitrides or antimonides.
Surface Science 149 (1985) 349-365 North-Holland, Amsterdam
349
THE ELECTRON MEAN FREE PATH (APPLICABLE TO QUANTITATIVE ELECTRON SPECTROSCOPY) H. T O K U T A K A ,
K. N I S H I M O R I
a n d H. H A Y A S H I
Department of Electronics, Faculty of Engineering, Tottori University, Koyama, Tottori, Japan Received 8 March 1984; accepted for publcation 27 August 1984
There are two well known methods accepted generally to establish the value of the electron mean free path. One is Seah's method where he compiled many published experimental data. The other is Penn's method which is extensively theoretical. Besides, Tarng and Wehner showed that there is a significant difference between the observed electron mean free paths, according to whether the electron pass through Mo or W. Here, we propose a general method to calculate the electron mean free path for material of any atomic number, using Tarng and Wehner's experimental results (Mo and W) and our experimental data for Cr. Then, we compare and review these three methods of Seah, Penn and ourselves to learn which method is the most accurate, using published AES and XPS experimental data. Among these three methods, our method shows values closest to the experimental ones. Finally, we must add the following sentence: When the AES experimental data are compared with the theoretical values, the attenuation length of the primary electron beam should be considered,
366
Surface Science 149 (1985) 366-380 North-Holland, Amsterdam
C A L C U L A T I O N O F T H E A T O M I C G E O M E T R I E S O F T H E (110) SURFACES OF IlI-V COMPOUND SEMICONDUCTORS C. M A I L H I O T
a n d C.B. D U K E
Xerox Webster Research Center, Bldg. 114, 800 Phillips Road, Webster, New York 14580, USA and
A13 D.J. C H A D I Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, California 94304. USA Received 20 June 1984 A total-energy minimization method, developed earlier, is applied to predict the minimum-energy atomic geometries of the (110) surfaces of GaP, GaAs, GaSb. InP. InAs and InSb. These predicted geometries are shown to be in excellent correspondence with those determined by elastic low-energy electron diffraction intensity analyses, The magnitude of the thermal rms displacements of the surface atoms are predicted to be comparable to those of bulk atoms in agreement with ion channeling experiments in GaAs(110).
Surface Science 149 (1985) 381-393 North-Holland. Amsterdam
381
C O M P E N S A T I O N EFFECTS IN T H E R M I O N I C E L E C T R O N E M I S S I O N R. VANSELOW Department of Chemistry and Laboratory for Surface Studies, Unioersity of Wisconsin - Milwaukee, Milwaukee, Wisconsin 53201. USA Received 10 May 1984; accepted for publication 11 September 1984 It could be demonstrated that, as in the case of thermionic ion emission [Pederson and Vanselow, Surface Sci. 135 (1983) 553; Vanselow and Pederson, Surface Sci. 140 (1984) 123]. thermionic electron emission can be described by
j = *j exp(q~/k*T) exp( - ~ / k T ) , w h e r e j is the current density, *j and *T are the isokinetic coordinates (*T ~- isokinetic temperature), and q~ is the work function. This description is subject to the usual assumptions as to the nature of work function and reflection coefficient. Using the experimentally determined (apparent) Richardson constant, ..4a, and work function, ,~,,, one obtains *
lnAa=2"69-2"51n
add?
~a
T+k--d-T+ k'T"
The latter is of the form of the classical compensation equation, which means that if the work function of a crystal face with given orientation { hkl} is altered by adsorption or by an external electric field, or if, for a given metal, clean crystal faces with different surface structures (different work functions) are considered, ]n A a versus ,~,, plots should yield straight lines. Using appropriate experimental (A a, ~a) pairs, this dependence could indeed be verified for all above mentioned cases. The slope of such a plot allows the calculation of the corresponding isokinetic temperature, *T. Using the m a x i m u m energy barrier height. ~a.ma*, for each homologous series, the corresponding entropy change, A*Se,,p = ~a.max/*T, can be calculated and compared with the theoretical Sackur-Tetrode entropy, A*St~¢or (for p = *p = 1 d y n / c m 2, T = *T and G = 2). It was found that, in general, A*S~p < A*Ztheor, which may indicate an influence of the temperature dependence of the work function. However, in most cases the deviations are only about 4% and. therefore, lie within the limits of error. The entropy values are of the order of 40 eu. As to be expected, the isokinetic temperature increases with ~ncreasing ~a,ma,,.
341 BONDS
T O N, P, As A N D Sb S T A T E S
a n d W i l l i a m A. G O D D A R D
OF
III
Arthur Amos Noyes Laboratory of Chemical Physics *, California Institute of Technology, Pasadena, California 91125, USA Received 25 June 1984; accepted for publication 25 September 1984 As a model for a proposed phosphine oxide-type initial state in the oxidation of III-V semiconductors, we have examined the structure and bonding of the phosphine oxide-type bond in CI 3Y = O where Y = N, P, As, ans Sb. We calculate an Y = O bond energy of 114 kcal for P = O, in reasonable agreement with experiment, 123 kcal/mol. The other calculated bond energies (kcal/mol) are 47 (N), 82 (As), and 63 (Sb). Based on these results, we conclude that such bonds should play an important role in phosphides and are likely to be important in arsenides but not in nitrides or antimonides.
Surface Science 149 (1985) 349-365 North-Holland, Amsterdam
349
THE ELECTRON MEAN FREE PATH (APPLICABLE TO QUANTITATIVE ELECTRON SPECTROSCOPY) H. T O K U T A K A ,
K. N I S H I M O R I
a n d H. H A Y A S H I
Department of Electronics, Faculty of Engineering, Tottori University, Koyama, Tottori, Japan Received 8 March 1984; accepted for publcation 27 August 1984
There are two well known methods accepted generally to establish the value of the electron mean free path. One is Seah's method where he compiled many published experimental data. The other is Penn's method which is extensively theoretical. Besides, Tarng and Wehner showed that there is a significant difference between the observed electron mean free paths, according to whether the electron pass through Mo or W. Here, we propose a general method to calculate the electron mean free path for material of any atomic number, using Tarng and Wehner's experimental results (Mo and W) and our experimental data for Cr. Then, we compare and review these three methods of Seah, Penn and ourselves to learn which method is the most accurate, using published AES and XPS experimental data. Among these three methods, our method shows values closest to the experimental ones. Finally, we must add the following sentence: When the AES experimental data are compared with the theoretical values, the attenuation length of the primary electron beam should be considered,
366
Surface Science 149 (1985) 366-380 North-Holland, Amsterdam
C A L C U L A T I O N O F T H E A T O M I C G E O M E T R I E S O F T H E (110) SURFACES OF IlI-V COMPOUND SEMICONDUCTORS C. M A I L H I O T
a n d C.B. D U K E
Xerox Webster Research Center, Bldg. 114, 800 Phillips Road, Webster, New York 14580, USA and
A13 D.J. C H A D I Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, California 94304. USA Received 20 June 1984 A total-energy minimization method, developed earlier, is applied to predict the minimum-energy atomic geometries of the (110) surfaces of GaP, GaAs, GaSb. InP. InAs and InSb. These predicted geometries are shown to be in excellent correspondence with those determined by elastic low-energy electron diffraction intensity analyses, The magnitude of the thermal rms displacements of the surface atoms are predicted to be comparable to those of bulk atoms in agreement with ion channeling experiments in GaAs(110).
Surface Science 149 (1985) 381-393 North-Holland. Amsterdam
381
C O M P E N S A T I O N EFFECTS IN T H E R M I O N I C E L E C T R O N E M I S S I O N R. VANSELOW Department of Chemistry and Laboratory for Surface Studies, Unioersity of Wisconsin - Milwaukee, Milwaukee, Wisconsin 53201. USA Received 10 May 1984; accepted for publication 11 September 1984 It could be demonstrated that, as in the case of thermionic ion emission [Pederson and Vanselow, Surface Sci. 135 (1983) 553; Vanselow and Pederson, Surface Sci. 140 (1984) 123]. thermionic electron emission can be described by
j = *j exp(q~/k*T) exp( - ~ / k T ) , w h e r e j is the current density, *j and *T are the isokinetic coordinates (*T ~- isokinetic temperature), and q~ is the work function. This description is subject to the usual assumptions as to the nature of work function and reflection coefficient. Using the experimentally determined (apparent) Richardson constant, ..4a, and work function, ,~,,, one obtains *
lnAa=2"69-2"51n
add?
~a
T+k--d-T+ k'T"
The latter is of the form of the classical compensation equation, which means that if the work function of a crystal face with given orientation { hkl} is altered by adsorption or by an external electric field, or if, for a given metal, clean crystal faces with different surface structures (different work functions) are considered, ]n A a versus ,~,, plots should yield straight lines. Using appropriate experimental (A a, ~a) pairs, this dependence could indeed be verified for all above mentioned cases. The slope of such a plot allows the calculation of the corresponding isokinetic temperature, *T. Using the m a x i m u m energy barrier height. ~a.ma*, for each homologous series, the corresponding entropy change, A*Se,,p = ~a.max/*T, can be calculated and compared with the theoretical Sackur-Tetrode entropy, A*St~¢or (for p = *p = 1 d y n / c m 2, T = *T and G = 2). It was found that, in general, A*S~p < A*Ztheor, which may indicate an influence of the temperature dependence of the work function. However, in most cases the deviations are only about 4% and. therefore, lie within the limits of error. The entropy values are of the order of 40 eu. As to be expected, the isokinetic temperature increases with ~ncreasing ~a,ma,,.