Luminescence from In0.5Ga0.5P prepared by vapor-phase epitaxy

Abstract

The photoluminescence from n‐ and p‐type In_1−xGa_xP with x≃0.5, prepared by vapor‐phase epitaxy on GaAs substrates, has been studied between 4.2 and 300 K. This material is of particular practical interest because of its close lattice‐parameter match with GaAs and direct energy band gap of 1.9 eV. At very low temperatures, four major emission bands have been identified, involving intrinsic recombination, donor—to—valence‐band transitions, conduction‐band—to—acceptor transitions, and donor‐acceptor transitions. The intrinsic recombination dominates in all the samples above about 150 K. The spectra are consistent with a shallow donor ionization energy of 7±1 meV, the same value as in InP. The spectral data of Cd‐doped samples (with p varying from 1.8×10¹⁶ to 9.3×10¹⁷ cm⁻³) suggest a consistent shift of the Cd acceptor ionization energy to lower values with increasing doping. The extrapolated value for very low doping is 59±2 meV at 50 K. The residual donor density is low in all the p‐type samples studied (≲ 10¹⁶ cm⁻³). In the case of highly p‐type Zn‐doped material, a major new emission band is seen 0.19 eV below the band‐gap energy at 77 K and may contribute to the low radiative efficiency of this material. The band is believed to be due to a complex center involving Zn. The photoluminescence data presented for Zn‐doped material indicate that the radiative efficiency falls off steeply with increasing doping at 300 K in In_0.5Ga_0.5P with p > 10¹⁸ cm⁻³, in contrast to the case of GaAs. The relevance of the present data to homojunction laser diode fabrication is discussed.