Calculation of the minority-carrier confinement properties of III-V semiconductor heterojunctions (applied to transmission-mode photocathodes)

For electro-optical device applications, the principal properties desired of a heterojunctions are minority-carrier confinement and a change in optical parameters. It is shown that for III-V materials with heavily doped junctions the minority-carrier confinement properties may be approximately calculated from the materials parameters by using a simple relationship. The critical parameters are shown to be the minority-carrier diffusion length, the device operating temperature, and the rate at which the band gap of a materials system varies with lattice constant. The effective interfacial recombination velocity into the high-band-gap side of a heterojunction is calculated from these parameters, and is in turn used to calculate the properties of transmission-mode III-V photocathode devices. Some materials systems such as GaAs–AlGaAs and InP–InGaAsP demonstrate near-ideal performance as photocathodes, while other commonly used materials systems such as GaAs–GaAsP are shown to be fundamentally incapable of good performance. A difference in electrical properties is demonstrated between liquid-phase-epitaxially grown heterojunctions and vapor-phase-epitaxially grown heterojunctions.