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

SHORTLY after the birth of quantum mechanics, von Neumann and Wigner made the remarkable proposal1 that certain spatially oscillating attractive potentials could support bound states at energies above the potential barriers (that is, spatially confined states within the continuum) by means of diffractive interference. Because of their unusual geometry, such potentials were regarded as mathematical curiosities2,3, although more recently it has been suggested that they might be found in certain atomic and molecular systems4,5. Following the observation of discrete electronic states in ultra-thin semiconductor layered structures6,7 (for example, in quantum wells), Stillinger8 and Herrick9 proposed that super-lattices might be used to construct potentials supporting these 'positive energy' bound states. Here we report direct evidence of such states in semiconductor heterostructures grown by molecular-beam epitaxy10. Infrared absorption measurements reveal a narrow, isolated transition from a bound state within a quantum well to a bound state at an energy greater than the barrier height; this state is spatially localized by Bragg reflections.

Observation of an electronic bound state above a potential well

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

Local fields in the electrodynamics of mesoscopic media

We report the first high‐detectivity (D*=1.0×1010 cm (Hz)1/2/W), high‐responsivity (Rv =30 000 V/W) GaAs/AlxGa1−xAs multiquantum well detector, sensitive in the long‐wavelength infrared band at λ=8.3 μm (operating at a temperature of T= 77 K). Because of the mature GaAs growth and processing technologies as well as the potential for monolithic integration with high‐speed GaAs field‐effect transistors, large focal plane arrays of these detectors should be possible.

High‐detectivity D*=1.0×1010 cm √H̄z̄/W GaAs/AlGaAs multiquantum well λ=8.3 μm infrared detector

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 report, for the first time, intersubband absorption experiments in doped InGaAs/InAlAs multiquantum well superlattices and observe a resonance peak at a wavelength of λ=4.4 μm which is in good agreement with theory. This material system may be useful for detectors in the λ=3–5 μm spectral region.

InGaAs/InAlAs multiquantum well intersubband absorption at a wavelength of λ= 4.4 μm

We have directly determined a high velocity (v=2×107 cm/s) for electrons in a submicron (0.42 μm), strongly graded (quasifield F=8.8 kV/cm) highly doped ( p=4×1018 cm−3) AlxGa1−xAs layer. A transit time of only 1.7 ps was measured (an order of magnitude shorter than that for F=1.2 kV/cm). Such a structure would be ideal for the low resistance base of a high‐speed n‐p‐n transistor.

D. A. Kleinman

Papers

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

InGaAs/InAlAs multiquantum well intersubband absorption at a wavelength of λ= 4.4 μm

Measurement of high electron drift velocity in a submicron, heavily doped graded gap AlxGa1−xAs layer