Intersubband Transitions in High Indium Content InGaAs / AlGaAs Quantum Wells Grown on GaAs with a Graded InGaAs Buffer

Abstract

Large intersubband transition energies are interesting for applications in quantum well infrared photodetectors (QWIPs) and nonlinear optical frequency conversion devices. QWIPs have recently been a topic of interest for applications in high speed detector arrays.1 By using large energy intersubband transitions in quantum wells, the useful range of these QWIPs can be extended to the 3-5μm atmospheric window. With the demonstration of large nonlinear optical susceptibilities in quantum wells,2 application of large intersubband transition energies to frequency conversion devices is also of interest. Large intersubband transition energies have been observed in GaAs / AlAs (E16 = 434meV)3 as well as InGaAs / InAlAs on InP quantum wells (E12 = 400meV for strained, E12 = 295meV for unstrained).4,5,6 By using pseudomorphic InGaAs / AlGaAs quantum wells, the conduction band offset AEC is further extended.7 However, the lattice mismatch of InGaAs and AlGaAs typically limits the range of indium content available. By using a compositionally graded buffer, Lord, et. al.8 have demonstrated that high quality In(0.5)Ga(0.5)As / AlGaAs quantum wells can be grown on a GaAs substrate. Using this novel growth technique, we report the first observation of intersubband transitions in high indium content InGaAs / AlGaAs quantum wells.