ABSTRACTWe report on intersubband transitions in InxGa1-xAs/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The conduction band offset for this material system is larger than that of the well known GaAs/AlGaAs system, thus making it possible to design, grow, and fabricate quantum well infrared photodetectors operational beyond the 14 μm spectral region with minimized dark current. We have grown InxGa1-xAs/AlGaAs MQWs with indium compositions ranging from x = 0.08 to 0.20 verified by in situ RHEED oscillations, band offset measurements, and high-resolution X-ray diffraction. Band-to-band transitions were verified by photoluminescence measurements, and intersubband transitions were measured using Fourier transform infrared (FTIR) spectroscopy. Due to the high strain and introduction of dislocations associated with the high indium content, wells with indium compositions above ∼ 0.12 did not result in intersubband transitions at silicon doping levels of 2×1018 cm-3. A thick linear graded InxGa1-xAs buffer was grown below the MQW structures to reduce the strain and resulting dislocations. Intersubband transitions were measured in InxGa1-xAs wells with indium compositions of x = 0.20 and greater when grown on top of the linear graded buffer. In addition to these results, FTIR measurements on InGaAs/AlGaAs MQW multi-color, long-wavelength infrared detector structures are reported.
