V/III ratio and silicon doping effects on the properties of In 1− xGa xP/GaAs grown by solid source molecular beam epitaxy

Abstract

We report the molecular beam epitaxial (MBE) growth of high quality In 1− x Ga x P epilayers grown on GaAs (1 0 0) substrate using a valved phosphorus cracker cell at a wide range of lattice mismatch, V/III flux ratio and silicon (Si) doping concentrations. Film characterization was carried out using X-ray diffraction (XRD), Raman scattering spectroscopy, low temperature photoluminescence (PL) and Hall effect measurements. The PL full-width at half-maximum (FWHM) measured at 10 K increased from ∼6.5 to ∼34 meV when the lattice mismatch increased from <10 −4 to 3.5 × 10 −3. Typical Raman spectrum showed features characteristic of disorder in the material with the appearance of GaP-like and InP-like longitudinal-optic (LO) modes and the transverse-optic (TO) mode. The PL peak energy increased from 1.941 to 1.964 eV while the PL FWHM decreased from ∼11.3 to ∼6.3 meV as the V/III ratio was increased from 5 to 50, indicating an increase in the disorder level (more random) and improvement in the optical quality. The clustering effect increases following a decrease in the V/III ratio, due to an increase in the level of ordering in the material. Within the range of silicon (Si) effusion cell temperature investigated (900–1200°C), the highest electron concentration obtained was 7.7 × 10 18 and 3.2 × 10 18 cm −3 at room temperature and 77 K, respectively. The concentration decreased with further increase in the silicon cell temperature. The Hall mobility at 300 K varied from 356 to 1720 cm 2/Vs within the range of electron concentration measured (4.5 × 10 16–7.7 × 10 18 cm −3). Except for the sample grown at the highest silicon cell temperature (1200°C), the PL spectrum of other samples showed a dominant peak attributed to Si donor-to-band transition (D–B), which shifted to higher energy following an increase in the electron concentration. The sample grown at the highest Si cell temperature showed a PL peak at ∼1.913 eV which was attributed to a transition between the conduction band and Si acceptor (B–A).