TRANSPORT PROPERTIES OF GAAS OBTAINED FROM PHOTOEMISSION MEASUREMENTS

Using the technique of high-resolution energy-distribution analysis of electrons photoemitted from a cleaved GaAs surface coated with a layer of Cs, we have been able to determine many of the transport properties of GaAs which are important in the operation of the GaAs-Ca-O photocathode and other GaAs devices. A two-minima diffusion model is presented which explains the photon energy dependence of the photocathode yield near threshold. Electron diffusion lengths for the Γ1 and X1 minima have been determined from the spectral shape of quantum yield as a function of temperature and carrier concentration for heavily doped p-type material. The hot-electron scattering length for equivalent intervalley scattering has been measured by comparison with a computer scattering model. The coupling constant for equivalent intervalley scattering has been calculated from the hot-electron scattering length. The coupling constant for scattering between the Γ1 and X1 minima is calculated from the X1 diffusion length. These results, along with other recent data, are used to calculate the temperature dependence of the mobility in the X1 valleys and the intervalley scattering time. The temperature dependence of the energy spacing of the Γ1 and X1 valleys has been measured. The escape probability for the photocathode and the shape of the energy distribution curves is explained by a model which includes optical phonon scattering in the band-bending region, reflection at the surface, trapping in surface states, and lifetime broadening. © 1969 The American Physical Society.