Effects of Zn and Ga interdiffusion on ZnSe/n⁺GaAs interfaces

Abstract

We report the results of optical and electrical measurements performed on two pseudomorphic ZnSe/n+GaAs heterojunctions in which the ZnSe was grown by molecular beam epitaxy. One of t h e ZnSe epilayers was doped as a p-n junction using Li and CI as dopants, with t h e layer adjacent to the interface doped n + ; the other was unintentionally doped. Our results determine uniquely the band profiles of both samples studied. Those band profiles clearly display t h e effects of Zn and Ga interdiffusion, which creates strong band-bending on both sides of the interlaces and creates in the GaAs a barrier against electron diffusion into t h e ZnSe. T h e presence and size of that barrier is of primary importance for ail ZnSeIGaAs device considerations. For each sample our measurements determine the height and depth of that barrier, the position of the bands at the interface relative to the Fermi level, and t h e built-in field on each side of the interface. From that information the magnitude and range of the Zn and Ga interdiflusion are determined.

New Theoretical Treatment of Electroreflectance from Surfaces and Interfaces Having Large Built-in Fields

“…Perhaps not surprisingly in light of the large number of adjustable parameters in our fits, for N, > 5 x 101 cm 3 we have obtained excellent fits to the ER data for all of the samples investigated. Figure 3 shows typical low-field-theory and high-field-theory fits to a sample with Nd = 1015.…”

“…Figure 4 shows fits to a sample with Nd -1.24 X 1017 cm 3 as measured by the Hall effect, with the fitting parameter Nd fixed at the values 101" cm 3 , 1.3 X 10 1 7 cm 3 and 1.6 X 1017 cm" 3 . The best fits for Nd = 1017 cm" 3 and for Nd -1.6 x 1017 cm" 3 are obviously inferior. For this sample, the best fit to the ER data was for Nd -1.28 x 1017 cm 3 , in excellent agreement with the value measured using the Hall effect.…”

“…To fit the high-field experimental results accurately using the high-field formalism described here requires 17 or 18 Band profile for n*CaAs with Nd -2.8 x 1010 cm" 3 showing the level quantization of the heavyhole band in the depletion region and two possible transitions from a quantized heavy-hole level to the conduction-band edge.…”

“…(6) i 7_ dc.W. 2 J' dcw, 3 Here, the sum over j goes over critical points and over discrete bound states for each minority band. By deriving approximate formulas for the ratios of the coefficients A, Bi and C, for different bound states and neglecting small terms, we were able to reduce the total number of unknown coefficients to 5 for the E, transition and 3 for the E 0 + A, transition.…”

“…Both numerical calculations and purely theoretical considerations show that even the best published general treatments 6 . 7 of the effects of high fields is invalid for n-doped materials with E, Ž lO V/cm (Nd Ž 10"7 cm" 3 for GaAs). Therefore, we have developed a new theoretical treatment of the modification of the local dielectric function by intense electric fields.…”