Electrical Properties of InGaP Doped with Si

Abstract

We measured Hall concentration n in InGaP:Si epitaxial layers grown by MBE as a function of pressure P up to 2 GPa and of temperature T from 77 to 300 K. We interpreted our results in terms of the broad distribution of impurity states resonant with the conduction band. From the low-temperature . n(P) dependence we can directly obtain the total density of impurity states around the Fermi level ρ(ΕF). The Fermi level can be shifted with respect to impurity states by applying pressure and by using samples with different n. In this way we obtain p(E) in a wide energy range. We discuss the possible reasons for the observed broad distribution of p(E).PACS numbers: 72.20. Fr, 72.80.Ey, 71.55.Eq InGaP lattice matched to GaAs (i.e. with 48% of indium) is an important material for red-emitting laser diodes. For the MBE growth of n-type InGaP the Si donor is commonly used. However, there is very little data in the literature concerning the electrical properties of this material. We have studied epitaxial layers (around 1 micron thick) of InGaP:Si grown by ALMBE and MBE on semi-insulating GaAs. Hall concentration n in our samples (at T = 300 K) varied from 2 x 10 17 cm -3 up to 5 x 10 18 cm -3 . In this range we are above the Mott transition and we can neglect the effect of surface states (it is believed that InGaP has a much lower density of surface states as compared to AlGaAs). We measured n and mobility μ as functions of pressure Ρ (up to 20 kbar) and temperature T (from 20 to 300 K) using the gas cell up to 1.2 GPa and the liquid cell for higher pressures. The temperature variation of electron concentration was rather weak and similar to the literature data interpreted as due to the ionization of shallow-impurity levels [1]. However, the pressure variation of Hall concentration was substantial. This definitely eliminates the shallow-impurity interpretation. In Fig. 1 we show the n(P) dependence at 77 K for three samples. As we can see, the concentration drops for each sample. The decrease in the electron concentration (431) .

Electrical Properties of InGaP:Si and AlGaAs:Sn Epitaxial Layers

“…Let us assume that rE does not change its shape but only shifts with respect to the conduction band with some coefficient dE d adp. Differentiating the condition of charge neutrality in the sample and expanding rE À E d around the Fermi energy E F we obtain [6] dn dp…”