Zn incorporation and band gap shrinkage in p-type GaAs

Abstract

Dimethylzinc (DMZn) was used as a p-type dopant in GaAs grown by low pressure metalorganic vapor phase epitaxy using trimethylgallium and arsine (AsH₃) as source materials. The hole carrier concentrations and zinc (Zn) incorporation efficiency are studied by using the Hall effect, electrochemical capacitance voltage profiler and photoluminescence (PL) spectroscopy. The influence of growth parameters such as DMZn mole fraction, growth temperature, and AsH₃ mole fraction on the Zn incorporation have been studied. The hole concentration increases with increasing DMZn and AsH₃ mole fraction and decreases with increasing growth temperature. This can be explained by vacancy control model. The PL experiments were carried out as a function of hole concentration (10¹⁷-1.5×10²⁰cm^-3). The main peak shifted to lower energy and the full width at half maximum (FWHM) increases with increasing hole concentrations. We have obtained an empirical relation for FWHM of PL, ΔE_p(eV) = 1.15× 10^-8p^1/3. We also obtained an empirical relation for the band gap shrinkage, ΔE_g in Zn doped GaAs as a function of hole concentration. The value of ΔE_g(eV) = -2.75× 10^-8p^1/3, indicates a significant band gap shrinkage at high doping levels. These relations are considered to provide a useful tool to determine the hole concentration in Zn doped GaAs by low temperature PL measurement. The hole concentration increases with increasing AsH₃ mole fraction and the main peak is shifted to a lower energy side. This can be explained also by the vacancy control model. As the hole concentration is increased above 3.8×10¹⁸cm^-3, a shoulder peak separated from the main peak was observed in the PL spectra and disappears at higher concentrations.