No abstract

We describe a new type of intersubband GaAs/AlGaAs infrared detector consisting of three stacks of quantum wells; the quantum wells in a given stack-are identical, but are different from stack to stack. Each stack is designed to yield an absorption and a photoresponse at a different peak wavelength. The resulting device is an infrared detector which can operate in a number of modes. Among the features of this device are a wide-band detection domain, a tunable response and excellent responsivities and noise figures. The tunable operation includes a sharp peak-switching response which follows the formation, expansion, and readjustment of electric field domains within the multiquantum well region.Intersubband quantum well detectors have recently been the subject of a considerable research effort;ld properties important for many applications are a wide spectral response,7 preferably over the atmospheric window 8-12 pm and tunability of the peak wavelength.s-"We report here on the operation of a new type of bound-to-continuum GaAs infrared detector, consisting of three different stacks of quantum wells arranged in series. All the wells in a given stack are identical, but each stack is designed for absorption and detection at a different wavelength, featuring distinct well widths and barrier heights.The detector can operate in one of a number of modes. At forward and low bias voltages, the response peaks at a single wavelength ( -1400 cm-') and the device functions as a standard bound-to-continuum infrared detector."'3 When exceeding a temperature-dependent critical applied voltage, the detector's spectral response switches to a different peak wavelength ( -1140 cm -'), while the detection at the previous peak is significantly reduced. At a reverse bias the detection is again centered on the higher energy peak ( -1400 cm-') up to a specific applied voltage; for moderately higher voltages, two peaks yield a significant photoresponse. At still higher values of the reverse voltage a third response peak appears, which results in operation as a wide-band detector. These features are accompanied by good responsivity and detectivity figures.The structure was grown by molecular beam epitaxy on a semi-insulating GaAs substrate. The superlattice, clad by two n-doped contact layers, consisted of three stacks of 25 quantum wells each; the first 25 wells were 3.9 nm wide and were separated by Alo,3sGac62As barriers; the second stack consisted of 25 quantum wells 4.4 nm wide with Alo,30Ga,,70As barriers; the last stack had 25 wells 5.0 nm wide and Alo.,,Gac76As barriers. All the barriers were 44 nm long; the wells and the contacts were uniformly doped with Si to n=4X lOI cmA3.The absorption at zero field and room temperature is shown in Fig.

Negative transconductance resonant tunneling field effect transistors and monolithically integrated resonant tunneling diodes

We describe the observation of phase conjugation at 10.6 μm in a GaAs/AlGaAs multi-quantum-well-doped structure. The responsible nonlinear susceptibility χ(3) is due to a nearly resonant intersubband transition. The magnitude of χ(3) is 7×10−5 esu and the phase conjugate reflectivity is a few tenths of a percent.

We report on the first observation of third-order intersubband nonlinearities in a quantum well structure. We have measured the dc Kerr effect in a symmetric quantum well and found that the Kerr coefficients due to intersubband transitions are six orders of magnitude larger than that of bulk GaAs. To our best knowledge this is the largest value ever measured for the third-order susceptibility. By including dc screening effects and evaluating the internal electric field in the well, a good agreement between the calculated coefficients and the experimental ones was found.