Gas Source Molecular Beam Epitaxy of ZnSe on (In,Ga)P

ABSTRACTThe wide bandgap semiconductor ZnSe has been nucleated on epitaxial (In,Ga)P buffer layers (on GaAs substrates) having various In compositions, and hence various lattice constants. The III-V ternary alloy offers a wide range of lattice constants for the heteroepitaxy of a multitude of potential II-VI light emitting devices, such as blue pn injection lasers composed of the (Zn,Mg)(S,Se) material system. Since the II-VI and III-V layers are grown using gas source molecular beam epitaxy in separate dedicated reactors, the technique of amorphous As deposition is employed to passivate the (In,Ga)P surface prior to the ex situ transfer. High resolution double crystal x-ray diffraction measurements on the ZnSe/(In,Ga)P/GaAs heterostructures indicate that for In compositions of 50-52%, the buffer layers with a thickness of 4 μm were only partially relaxed on the GaAs substrates, with the residual mismatch remaining at the ZnSe/III-V heterointerface. The critical thickness of (In,Ga)P, with In concentrations near 52-56%, on GaAs greatly exceeds the predicted critical thickness from either the energy balancing or force balancing model. For an In composition of 56% (and a film thickness of 4 μm), the buffer layers contain an in-plane lattice constant equal to that of ZnSe, and therefore represent the lattice-matched condition, even though the film is not fully relaxed. For (In,Ga)P buffer layers lattice-matched to ZnSe, but mismatched to GaAs, the surface exhibits the expected cross-hatched surface morphology. The occurrence of the cross-hatched surface is significantly alleviated by the addition of a pseudomorphic layer of GaAs positioned between the ZnSe and (In,Ga)P layer.