LPE GaAs/(Ga, Al)As/GaAs transmission photocathodes and a simplified formula for transmission quantum yield

Abstract

GaAs/(Ga,Al)As/GaAs transmission photocathodes were fabricated by a multiple layer liquid epitaxy technique using GaAs substrates. The GaAs substrate was subsequently removed by bubble etching. Transmission mode white light sensitivity of 340 μA/lm and an electron diffusion length of 5 μm or more can be routinely achieved. The reflection sensitivity was found to be lower than that of a similarly prepared layer grown directly on the GaAs substrate. The spectral response, when analyzed with the yield formula, indicated negligible recombination at the GaAs / (Ga,Al)As interface. Also, despite the almost perfect lattice match between GaAs and AlAs, some bowing of the GaAs / (Ga,Al)As samples was observed, suggesting the presence of internal stresses. A simplified formula is derived for the transmission quantum yield which enables graphic solution of surface recombination velocity at the photocathode input surface and the ratio of photocathode thickness to the electron diffusion length without tedious computer calculations.

Comparative research for GaAs photocathodes with graded compositional Al x Ga 1−x As buffer layer

“…Within the limitation of epitaxial grown technique, the approximately exponential-doping structure is actually a special kind of gradientdoping structure. The main difference on the active layer of two samples is that the standard sample has the thickness of 1.8 μm which has been approved to obtain higher quantum efficiency in early research and the mixed sample has the thickness of only 1.0 μm which can make the photo-excited electrons in window layer to arrive at the bottom of surface barrier layer [5][6][7][8]. For both samples, the Zn doping concentrations of the Al x Ga 1 À x As window layers are designed as 1 Â 1019 cm À 3 and the total thicknesses are same 0.5 μm.…”

“…3. For the SPV are mainly caused by the electron hole separation while absorbing photon energy, so in order to shield off the influence of Al x Ga 1 À x As buffer layer, the SPV curve was measured from 550 nm to 950 nm for that the Al x Ga 1 À x As window layer can be seemed as fully passing band in this wavelength range [2][3][4][5][6].…”

“…3, the Al x Ga 1 À x As window layer has almost no absorption between 400 nm and 550 nm, thus the surface photovoltage caused by the photo-excited electrons separation is mainly caused by the photo-excited electrons in active layer. So the fitting equations of SPV and SRC can be shown as the following equations [2][3][4][5][6][7][8].…”

Comparative research on reflection-mode GaAs photocathode with graded AlxGa1−xAs buffer layer

“…2, and the surface photo voltage (SPV) is mainly depended on the electron-hole separation while absorbing photon energy. Thus in order to shield off the influence of Al x Ga 1 À x As buffer layer at the short wavelength band from 400 nm to 550 nm, the SPV curve was only measured form 550 nm to 950 nm, where the buffer layer can be seemed as fully window layer with no photon absorption [2][3][4][5][6].…”

“…In this paper, in order to deeply study the impact of Al x Ga 1 À x As buffer layer for reflectionmode GaAs photocathodes, we carried out the comparative research between the surface photovoltage (SPV) before Cs-O activation and spectral response current (SRC) after Cs-O activation. The fitting equations and comparative research results can help to optimize the structure design and study the influence of graded Al compositional Al x Ga 1 À x As buffer layer in later research [2][3][4][5][6].…”