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

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Abstract
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.