I. Gravé

Voltage‐controlled tunable GaAs/AlGaAs multistack quantum well infrared detector

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.

Observation of third‐order intersubband dc Kerr effect at the midinfrared wavelengths in GaAs quantum wells

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.

Observation of phase conjugation at 10.6 μm via intersubband third-order nonlinearities in a GaAs/AlGaAs multi-quantum-well structure

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.

Monolithic integration of a resonant tunneling diode and a quantum well semiconductor laser

A monolithic integration of a double barrier AlAs/GaAs resonant tunneling diode and a GaAs/AlGaAs quantum well laser is reported. Negative differential resistance and negative differential optical response are observed at room temperature. The device displays bistable electrical and optical characteristics which are voltage controlled. Operation as a two‐state optical memory is demonstrated.

Control of Electric Field Domain Formation in Multiquantum Well Structures

The formation, expansion, and readjustment of electric field domains in multiquantum well stacks is described and explained in terms of sequential resonant tunneling. These effects are used to control the multiband spectral response in IR detector applications of these structures.

Microampere threshold current operation of GaAs and strained InGaAs quantum well lasers at low temperatures (5 K)

The operation of ultralow threshold current GaAs and InGaAs quantum well lasers at cryogenic temperatures has been studied. In particular the threshold current Ith and lasing wavelength of GaAs and strained InGaAs lasers have been measured as a function of temperature from 300 down to 5 K. Ith can in both lasers be characterized by a linear function of temperature up to 200 K, with a significantly (2.5×) larger dIth/dT for the GaAs laser. We measured a minimum threshold current of 120 μA for the GaAs laser and 165 μA for the InGaAs laser at 5 K. We derive a simple expression for the transparency carrier density as a function of temperature and effective masses to explain our results.

Demonstration of the optical Kerr effect at 10.6 μm via intersubband nonlinearities in a multi‐quantum well structure

We demonstrate the optical Kerr effect at 10.6 μm in a GaAs/AlGaAs multi‐quantum well doped structure. The effect is due to the nonlinear susceptibility χ(3) near a resonant intersubband transition.

Single‐mode very wide tunability in laterally coupled semiconductor lasers with electrically controlled reflectivities

Tunable, single longitudinal mode spectrum of a novel monolithic, laterally coupled semiconductor stripe laser has been demonstrated. A tuning range of 14.2 nm, which is the widest observed so far in a monolithic device, has been achieved.

Fundamental Limits in Quantum Well Intersubband Detection

Since the concept of infrared (IR) photodetection by intersubband absorption in superlattices was first proposed and demonstrated by Smith et al.(1), the field of intersubband physics and applications has grown and attracted an increasing interest. Along with the demonstration and the analysis of intersubband absorption(2), came the possibility of studying a very basic quantum system in the laboratory. These efforts revealed the richness of intertweened basic physical effects that have to be understood or taken into account for the full mastering of intersubband physics and applications: Stark(3), depolarization(4,5) and other energy shifts, exchange interactions in doped quantum wells(6), effects of real material systems, polarization(7) and parity selection rules - just to name a few. On the application side another important channel of interest was opened with the realization that very large optical nonlinearities could be achieved through intersubband transitions in superlattices(8-10).

Resonant tunneling through low dimensional quantum structures

Tunneling mechanism in zero‐ and one‐dimensional quantum structures is studied. Several new results, peculiar to low dimensions, are predicted. We find that subband mixing and multichannel tunneling induce the appearance of new tunneling channels with unusual interference patterns, and allow for longer lifetime of the resonances at higher energies in various channels. It is shown that in low dimensions, there exists a critical size of the structure below which the resonance nature of the tunneling process is diminished. In zero and one dimensions, there exists a critical magnitude of the confinement potential, below which there are no resonances in the transmission function for any size of the well. Negative differential resistance and other phenomena related to the resonance characters of the tunneling will not appear in this case. We also develop a generalized transfer matrix method that takes into account subband mixing; this formalism can be used to describe any transport problem in low dimensions.