A normal-incidence type-II quantum-well infrared photodetector using an indirect AlAs/Al0.5Ga0.5As system grown on (110) GaAs for mid- and long-wavelength multicolor detection

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Abstract
A normal‐incidence type‐II indirect AlAs/Al0.5Ga0.5As quantum‐well infrared photodetector grown on (110) GaAs by molecular‐beam epitaxy for mid‐ and long‐wavelength multispectrum detection has been developed. The normal‐incident excitation of long‐wavelength intersubband transition was achieved in the [110] X‐band‐confined AlAs quantum wells. Six absorption peaks including four from X‐band to Γ‐band intersubband resonant transitions were observed at wavelengths, λp1−6=2.2, 2.7, 3.5, 4.8, 6.5, and 12.5 μm. The resonant transport from X band to Γ band gives rise to high photoconductive gain, which is highly desirable for focal plane arrays image sensor applications.