(The) electrical and optical characteristrics of carbon doped GaAs epilayers grown by low pressure MOCVD

Abstract

The carbon (C) doping characteristics of GaAs epilayers have been investigated by varying the growth parameters of V/III ratio and growth temperature. Heavily carbon doped GaAs epilayers were obtained by reducing the V/III ratio down to 1 or using $CCl_4$ gas sources. All epilayers were grown by low-pressure and atmospheric-pressure metalorganic chemical vapor deposition (MOCVD). The temperature dependence of electrical properties of C doped GaAs epilayers have been investigated by Van der Pauw Hall analysis. The empirical relation of Hall mobility appropriate for C doped GaAs was obtained using the simple expression by Hilsum with some modified parameters. For C doped GaAs epilayers of p of $4.25\times{10^{19}}\;cm^{-3}$ and $1.01\times10^{20}\; cm^{-3}$, the mobilities were nearly constant at low temperature range ($T<100$ K), however they were decreased at high temperature range ($T>100$ K) due to optical phonon scattering. The temperature dependence of mobility has been analyzed using a simple analytical equation in degenerate limit and constant effective mass. There was no compensation in C doped GaAs epilayer of p of $4.25\times10^{19}\; cm^{-3}$, however there was a little compensation ($N_d/N_a=0.02$) in the epilayer with heavy doping concentration of $p=1.01\times10^{20}\; cm^{-3}$. The (400) diffraction peak of the C doped GaAs epilayer was splitted from the substrate GaAs peak. The measured angular separation was 191.25 arc sec for C doped GaAs with hole concentration of $9\times10^{19}\; cm^{-3}$. The lattice constant decreased with increasing the hole concentration due to strain by the incorporation of carbon, which has a smaller covalent radius than gallium and arsenic. The relationship between the hole concentration and the critical layer thickness ($L_c$) by the excess stress and Matthews- Blakeslee model was also discussed. It was calculated for both pure case and 10 \% compensated case. The excess stress model is more agreeable for C doped GaA...