Epitaxial GaAs and $GaAs_{1-x}P_x$ are grown on (100) GaAs substrate in $Ga-HCl-AsH_3-PH_3-H_2$ system. The effect of growth parameters such as temperature, partial pressure of reactant gases on the surface morphology, carrier concentration and compensation ratio are investigated. Surface morphology depends on the mole ratio of Ga to As (or P) in the vapor phase. When $P_{Ga}/P_{As}$ is 0.75 during GaAs growth, it shows defect free surface without hillocks or pits at the growth rate of 20-30μm/hr. In $GaAs_{1-x} P_x$, cross hatch pattern having orthogonal arrays appears on the surface due to the lattice mismatch between $GaAs_{1-x}P_x$ and GaAs.
Carrier concentration and mobility have a close relationship with the growth parameters. The typical values of them are $1.75\times10^{15}cm^{-3}$, 6,600 $cm^2$/V-sec at room temperature, and $1.45\times10^{15}cm^{-3}$, 25,800 $cm^2$/V-sec at 77˚k and compensation ratio $N_A^-/N^+_D$ ranges from 0.5 to 0.85.
The relation between the direct Γ-band energy of $GaAs_{1-x}P_x$ and phosphorus concentration, X is obtained experimentally as $E_Γ(X)=1.435 + 0.865X + 0.210X^2 $(eV) 300˚K. Isoelectronic impurity, nitrogen, in $GaAs_{1-x}P_x$ is also investigated by using photovoltage measurement. Experimentally measured electron mobility is fitted to the theoretical value taking all scattering mechanisms into consideration, in order to obtain impurity concentration($N_I$) and space charge factor ($N_sQ$).
