VPE Growth of III/V Semiconductors

Abstract

In recent years research on the epitaxial growth of IIIjV alloys has con­ centrated on those systems capable of producing lattice-matched hetero­ structures. The most important alloy of this type is AlxGal-xAs because the nearly exact lattice-parameter match between GaAs (ao = 5.654) and AlAs (ao = 5.661) allows the growth of lattice-matched heterostructures with nearly ideal interfaces and direct bandgap energies covering an important range for optoelectronic devices from 1 .43 to ,.., 2.0 eV. Other systems for which the lattice parameter of the epilayer can be made to match that of the substrate at a given composition such as GaxInl-xP / GaAs, or for a range of compositions, such as GaxIn 1 xAsyP 1 y/InP, are in much earlier stages of development. The ability to grow high quality lattice-matched AlxGa1-xAs heterostructures has resulted in dramatic improvements in the performance of such optoelectronic devices as lasers, high radiance IR LEDs for optical communication applications, visible LEDs, and integrated optics elements and circuits (1). In addition, two-layer devices where the top AlxGal-xAs layer acts to reduce surface recombination and to transmit effectively bandgap light to the junction have resulted in solar cells with air mass zero efficiencies of 19% (2) versus 14% for the best Si devices. If these could be produced cheaply, they could have significant impact on the feasibility of terrestrial photo voltaic solar energy converSlOn. A number of techniques used for the epitaxial growth of IIIjV semi­ conductors might be applied to the growth of AlxGal-xAs, including liquid phase, vapor phase, and molecular beam expitaxial growth (LPE, VPE, and MBE, respectively). Nearly all of the devices listed above are fabricated in AlxGal-xAs grown by the LPE technique. The LPE tech­ nique for a multilayer structure consists of a series of individual growth