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 ${\Gamma }_1$ and $X_1$ 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 ${\Gamma }_1$ and $X_1$ minima is calculated from the $X_1$ diffusion length. These results, along with other recent data, are used to calculate the temperature dependence of the mobility in the $X_1$ valleys and the intervalley scattering time. The temperature dependence of the energy spacing of the ${\Gamma }_1$ and $X_1$ 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.