Decrease of Modfet channel conductivity with increasing sheet electron concentration

The great decrease of electron mobility with increasing sheet electron concentration ns in modulation-doped AlGaAs/GaAs/AlGaAs quantum wells is observed. This effect is explained by increasing scattering of degenerated electrons by polar optical phonons. At ns >10 15 m -2 , the mobility decrease exceeds the increase of ns, and the channel conductivity decreases with increasing ns

Non-uniformly doped graded-gap Al(x)Ga(l-)xAs X-ray detectors with high photovoltaic response

Graded-gap AlxGa1-xAs/GaAs X-ray detectors with photovoltaic response have been designed and fabricated. A charge collection efficiency of 100% has been achieved in an AlxGa1-xAs layer with a thickness of 15 mum without application of any bias voltage to the layer. Experimentally, the measured sensitivity achieves 0.9 A/W. Amplification of the photocurrent takes place in the thin (15 mum) AlxGa1-xAs layer, and an efficiency of 5 x 10(5) V/W is attained at an absorbed power of 10(-7) W. The possibilities of using the new detectors for observation of X- ray images are considered

Graded-gap AlxGa1-x as X-ray detector with collected charge multiplication

An increase in sensitivity of the graded-gap AlxGa1-As-x/GaAs X-ray detectors is achieved using multiplication of charge generated in a detector body. A thin n-GaAs layer was grown on a narrow-gap side of the AlxGa1-As-x structure. This layer is used as a photoconductor. The multiplication of the charge injected from the graded-gap structure to the photoconductive n-GaAs layer exceeds a few hundred times. This sensitive structure was tested as a detector of single alpha particles (from an Am-241 source)

Optical response of the graded-gap AlxGa1-xAs X-ray detector

It has been observed that only a part of the AlxGa1-xAs graded- gap layer with the energy gap gradient g gt 20 eV/cm is active as a X-ray luminescence source. The thickness of the active layer is 30-50 mum. To increase the detectors optical response efficiency, the following methods are proposed and tested: 1. Reflection of the X-ray luminescence light, generated in the bulk AlxGa1-xAs layer, inside the total reflection angle theta; 2. Optical stimulation of the electron-hole radiative recombination