R. E. Doezema

Determination of the concentration and temperature dependence of the fundamental energy gap in AlxIn1−xSb

We use transmission spectroscopy to determine the energy gap for the AlxIn1−xSb alloy system in the Al concentration range from 0% to 25% from cryogenic to room temperature. The samples are epitaxial layers grown by molecular beam epitaxy on GaAs substrates. Our room temperature results are compared to those from two earlier studies. In our Al concentration range, we find a linear change of energy gap with alloy lattice constant.

Electrical properties of InSb quantum wells remotely doped with Si

Two-dimensional electron systems were realized in InSb quantum wells with AlxIn1−xSb barrier layers δ-doped with Si. Measured electron mobilities in multiple-quantum-well structures were as high as 41 000 cm2/V s at room temperature and 209 000 cm2/V s at 77 K. Simple models can be used to explain the observed dependencies of the electron density on the quantum-well-to-dopant distance and on the number of quantum wells. Characterization by atomic force microscopy indicates that layer morphology may be a factor limiting electron mobility.

Observation of excitonic transitions in InSb quantum wells

We report the observation of interband exciton transitions in InSb/AlxIn1−xSb multi-quantum-well samples. The exciton peaks are identified with the use of a simple quantum well model. The strain present in the InSb wells alters the spectrum significantly from that for unstrained III–V materials and makes it possible to use the exciton spectrum in determining the band offset.

Band offset determination in the strained-layer InSb/AlxIn1−xSb system

We use interband exciton transitions in parabolically graded quantum wells to measure the band offset at the InSb/AlxIn1−xSb interface. The method we use is based on similar studies in the GaAs/AlxGa1−xAs system but modified to reflect the strong nonparabolicity and strain of the InSb/AlxIn1−xSb system. We find a conduction band offset ratio of 0.62±0.04 for Al concentrations in the range 2%–12%. The observed lack of variation of the offset with Al concentration suggests a lack of strain dependence in the InSb/AlxIn1−xSb system for practical Al concentrations.

Electronic characterization of InSb quantum wells

Abstract We have fabricated InSb quantum-well structures with high electron mobilities that are limited by scattering due to crystalline defects and remote ionized Si dopants. The integer quantum Hall effect is observed in these structures and has an unusual temperature dependence. Interband exciton transitions in a parabolic quantum well are used to determine an InSb/Al 0.09 In 0.91 Sb conduction-band offset ratio of 57%±2%.

Exciton determination of strain parameters in InSb∕AlxIn1−xSb quantum wells

Excitons in semiconductors can be used as a tool to probe various material and structural properties. The authors studied strain-related materials parameters in InSb∕AlxIn1−xSb quantum well structures. By changing the Al concentration in the barrier layers (0.03<x<0.23), the strain in the quantum wells can be tuned continuously. Using infrared transmission measurements, the authors traced strain-induced shifts in the energies of the confined states. The different strain dependences of the light- and heavy-hole band edges allow us to determine deformation potentials α and β simultaneously.

Determination of deformation potentials in strained InSb quantum wells

We use interband exciton transitions in InSb∕AlxIn1−xSb multi-quantum-well samples to determine the heavy-hole and light-hole energy gaps as the strain is varied using Al concentrations up to 25%. The gaps are compared to deformation-dependent calculations of the energy gaps in the presence of biaxial strain to obtain a measure of the deformation potentials α and β.

High intensity submillimeter photoresponse of a Si inversion layer

The submillimeter wave (496, 385, and 66 μm) photoresponse has been measured in an n‐channel Si metal‐oxide‐semiconductor field‐effect transistor at 4.2 K. A fast (≤10 ns) response is observed only in the low carrier density (ns) regime where the dc conductance is activated. Nonlinear photo response is found for I≥10 kW/cm2 and the signal follows a simple saturation behavior. The peak illuminated effective mobility is ∼13 000 cm2/Vs (at ns∼0.7×1011 cm−2) which is more than a factor of 2 larger than the peak 4.2‐K mobility of the device (at ns∼2.4×1012 cm−2). At carrier densities greater than 5×1011 cm−2 the response is bolometric with a response time ∼1 μs.

Interband magneto-spectroscopy in InSb square and parabolic quantum wells

We measure the magneto-optical absorption due to intersubband optical transitions between conduction and valence subband Landau levels in InSb square and parabolic quantum wells. InSb has the narrowest band gap (0.24 eV at low temperature) of the III–V semiconductors leading to a small effective mass (0.014 m0) and a large g–factor (−51). As a result, the Landau level spacing is large at relatively small magnetic fields (<8 T), and one can observe spin-splitting of the Landau levels. We examine two structures: (i) a multiple-square-well structure and (ii) a structure containing multiple parabolic wells. The energies and intensities of the strongest features are well explained by a modified Pidgeon-Brown model based on an 8-band k•p model that explicitly incorporates pseudomorphic strain. The strain is essential for obtaining agreement between theory and experiment. While modeling the square well is relatively straight-forward, the parabolic well consists of 43 different layers of various thickness to appr...

Magneto‐Optical Properties of InSb Semiconductor Heterostructures

We have theoretically and experimentally studied the spin‐dependent Landau levels for electrons and holes in narrow‐gap InSb/AlInSb quantum well systems. We use the envelope function approximation for the electronic and magneto‐optical properties of InSb/AlInSb. Our model includes the conduction electrons, heavy holes, light holes and spin‐orbit split‐off holes for a total of 8 bands taking spin into account. The Pidgeon‐Brown model is generalized to include the effects of confinement in the quantum wells. In addition, strain effects are taken into account by assuming pseudomorphic growth conditions. Comparing our calculated electronic structures with experimental magneto‐absorption measurements, we obtain excellent agreement. Our results demonstrate that in addition to the major transitions, strong band mixing in the narrow gap material leads to several optical transitions which normally are forbidden.