Design, fabrication, and testing of intersubband infrared photodetectors operating at wavelengths between 2 ųm and 17 ųm

Intersubband (ISB) photon detectors based on photon – electron interactions between quantized electron subbands in the conduction band of semiconductor heterostructures are presented. As opposed to interband devices, the operating wavelength of ISB devices is set by choosing appropriate layer thicknesses of the heterostructure and is not fixed by the semiconductor material system. As only electrons are involved in ISB detection, ISB detectors are potentially faster compared to semiconductor interband detectors involving both conduction and valence band; the speed of the latter is limited by the slower holes in the valence band. This work focuses on novel quantum cascade detectors (QCDs). In contrast to common photoconductive ISB photodetectors, QCDs do not require an external bias voltage due to their asymmetric conduction band profile. This results in a favorable noise behavior, reduced thermal load, and simpler readout circuits. Several QCDs with detection wavelengths ranging from 2 µm to 17 µm are designed, grown, processed, characterized, and discussed. Using the In0.53Ga0.47As / In0.52Al0.48As semiconductor system, QCDs detecting at 17 µm, 10 µm, 7.5 µm, and 4.7 µm are presented. The specific detectivity D* of the 17 µm QCD is 11011Jones at an operating temperature of 5 K; this result is close to the background limited D*BLIP=1.41011 Jones at 17 µm. As the shortest ISB wavelength between bound states in a heterostructures is determined by the conduction band offset at the interface between two semiconductors, In0.53Ga0.47As / In0.52Al0.48As QCDs can only be realized down to about 4.5 µm. To obtain shorter wavelengths, QCDs based on two alternative semiconductor heterostructures are presented. An In0.61Ga0.39As / In0.45Al0.55As QCD operating at 4 µm is demonstrated. At 100 K, its specific detectivity is D*=1.91011 Jones. This value compares favorably to commercial semiconductor photodetectors in this wavelength range; at 4 µm, the common MCT detectors reach specific detectivities around 11011 Jones at operating temperatures of 77 K. To obtain even shorter wavelengths, InAlAs is replaced by AlAs0.56Sb0.44. Based on this system, a QCD detecting at 2 µm is presented.

Thèse de doctorat : Université de Neuchâtel, 2007 ; Th.1982