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.

© 1993 Optical Society of America