Deep levels in lattice-matched Ga0.51In0.49P/GaAs heterostructure have been investigated by thermal-electric effect spectroscopy (TEES) and temperature-dependent conductivity measurements. Four samples were grown by molecular-beam epitaxy with various phosphorus (P2) beam-equivalent pressures (BEP) of 0.125, 0.5, 2, and 4×10−4 Torr. A phosphorus vacancy (VP) -related deep level, an electron trap, was observed located at EC−0.28±0.02 eV. This trap dominated the conduction-band conduction at T≳220 K and was responsible for the variable-range hopping conduction when T<220 K. Its concentration decreased with the increasing phosphorous BEP. Successive rapid thermal annealing showed that its concentration increased with the increasing annealing temperature. Another electron trap at EC−0.51 eV was also observed only in samples with P2 BEP less than 2×10−4 Torr. Its capture cross section was 4.5×10−15 cm2. This trap is attributed to VP-related complexes.

Separate confinement heterostructure single quantum well GaAs/AlGaAs lasers with n-type modulation doped active regions are studied. Quantum well absorption is significantly modified by n-type modulation doping. The effects of modulation doping on transparency current density and threshold current density are determined. Modulation doping is shown to reduce transparency current density, thereby also reducing threshold current density. Threshold current densities are reduced by 30%, to values of less than 150 A/cm2 for long cavities. The effects on distributed loss and differential gain are also reported. No degradation of laser performance is observed due to the location of the electrical junction away from the active region or due to free carrier absorption loss. Heavily modulation doped structures lase on the second quantized state.

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