We demonstrate a novel 10.8 μm superlattice infrared detector based on doped quantum wells of GaAs/AlGaAs. Intersubband resonance radiation excites an electron from the ground state into the first excited state, where it rapidly tunnels out producing a photocurrent. We achieve a narrow bandwidth (10%) photosensitivity with a responsivity of 0.52 A/W and an estimated speed of 30 ps.

New 10 μm infrared detector using intersubband absorption in resonant tunneling GaAlAs superlattices

Analytic forms of the linear and the third-order nonlinear optical intersubband absorption coefficients are obtained for general asymmetric quantum well systems using the density matrix formalism, taking into account the intrasubband relaxation. Based on this model, we calculate the electric field dependence of the linear and the third-order nonlinear intersubband optical absorption coefficients of a semiconductor quantum well. The energy of the peak optical intersubband absorption is around 100 meV (wavelength is 12.4 μm). Thus, electrooptical modulators and photodetectors in the infrared regime can be built based on the physical mechanisms discussed here. The contributors to the nonlinear absorption coefficient due to the electric field include 1) the matrix element variation and 2) the energy shifts. Numerical results are illustrated.

Calculation of linear and nonlinear intersubband optical absorptions in a quantum well model with an applied electric field

We have measured the infrared intersubband absorption at 8.2 μm in doped GaAs/AlAs quantum well superlattices. Waveguide geometry experiments demonstrate strong absorption with 95% of the incident infrared energy being absorbed.

Strong 8.2 μm infrared intersubband absorption in doped GaAs/AlAs quantum well waveguides

We have observed Stark shifts of quantum well intersubband transitions in a perpendicular electric field. Two samples consisting of 100 and 120 A GaAs quantum wells separated by 350 A AlGaAs barriers showed optical absorption peaks at 11.1 and 13.9 μm, respectively. In an electric field of 36 kV/cm, the 13.9 μm peak shifted to 13.7 μm and the 11.1 μm shifted to 11.0 μm, in good agreement with theoretical calculations. These tunable transitions can be applied to high‐speed infrared light modulators.

Observation of Stark shifts in quantum well intersubband transitions

We present a detailed and thorough study of a wide variety of quantum well infrared photodetectors (QWIPs), which were chosen to have large differences in their optical and transport properties. Both n- and p-doped QWIPs, as well as intersubband transitions based on photoexcitation from bound-to-bound, bound-to-quasi-continuum, and bound-to-continuum quantum well states were investigated. The measurements and theoretical analysis included optical absorption, responsivity, dark current, current noise, optical gain, hot carrier mean free path; net quantum efficiency, quantum well escape probability, quantum well escape time, as well as detectivity. These results allow a better understanding of the optical and transport physics and thus a better optimization of the QWIP performance.

Photoexcited escape probability, optical gain, and noise in quantum well infrared photodetectors

A new mode of IR detection using photoemission from a single quantum well is proposed and optimization of the device performance by the proper choice of parameters is discussed. Despite the very thin device structures, theoretical calculations show large absorption at wavelengths near cutoff. The largest photoemissive response is found by adjusting the well parameters so that an excited virtual state lies just above threshold.

D. D. Coon

Papers

New mode of IR detection using quantum wells