4500PQ01 - Quantum Well Absorption Quantum well infrared...

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Unformatted text preview: Quantum Well Absorption Quantum well infrared photodetectors (QWIP’S) operate by the absorption of light by quantum wells in semiconductor materials. A gallium arsenide (GaAs) quantum well of thickness d is contained within a slab of gallium aluminum arsenide (GaAlAs) as shown below. Light of wavelength A is absorbed by exciting an electron from a lower energy state of the quantum well to a higher energy state of the quantum well. The ab— sorption of the light is proportional to (Ft - 2)2d5 where (E - :2) is the component of the polarization of the refracted wave that is perpendicular to the quantum well (along the growth direction or z direction). Therefore TE polarized light is not absorbed since the optical electric field is entirely parallel to the quantum well interface (no component along the z direction). Only TM polarized light is absorbed since it has a component of the optical electric field along the z direction. The quantity dB is the path length of the light crossing the quantum well and d3 = d/cosfi. For a GaAs-quantum-well/gallium-aluminum-arsenide slab (n2 2 3.66) in air (711 = 1), determine the angle of incidence, aabsor, that produces the maximum absorp— tion (and thus the largest photocurrent in the QWIP). In the analysis, include reflection and refraction at the upper air-GaAlAs boundary. Neglect reflections from the lower GaAlAs—air boundary. Numerical methods are suggested to be appropriate. Express aabsor accurately to the nearest degree. Put your final answer in the space provided. aabsor — ...
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