G. Halkias

Photoreflectance studies of lattice‐matched and strained InGaAs/InAlAs single quantum wells

Lattice‐matched and strained InxGa1−xAs/In0.52Al0.48As single quantum wells with x=0.53 and x=0.60 have been studied by the optical modulation technique of photoreflectance (PR) at room temperature. The measurements have allowed the observation of interband transitions from the heavy‐ and light‐hole valence subbands to the conduction subbands. The PR data have been adjusted with a least‐squares fit to the first‐derivative functional form. The energetic positions of the optical transitions deduced from the fit have been compared with theoretical values obtained by an envelope function model calculation including strain effects. The best adjustment allowed the determination of the conduction‐band offset parameter Qc which is found equal to 0.71±0.07 for the lattice‐matched and strained compositions.

Electric‐field dependence of interband transitions in In0.53Ga0.47As/In0.52Al0.48As single quantum wells by room‐temperature electrotransmittance

Room‐temperature electrotransmittance has been used in order to investigate the interband excitonic transitions in a 250‐A‐thick In0.53Ga0.47As/In0.52Al0.48As single‐quantum‐well system as a function of an externally applied electric field. Parity forbidden transitions, involving conduction‐band states with quantum numbers up to n=5, which become more pronounced at high electric fields were observed. The ground‐state and the forbidden transitions showed a significant red shift due to the quantum confined Stark effect. A comparison with previously reported results on thinner InGaAs/InAlAs quantum wells indicated that the wide‐well sample exhibits the largest shift, as expected from theory. Despite the appreciable Stark shift, the rather large, field‐induced linewidth broadening and the relatively low electric field at which the ground‐state exciton is ionized poses limitations on using this wide‐quantum‐well system for electro‐optic applications.

A Comprehensive Optimization of InAlAs Molecular Beam Epitaxy for InGaAs / InAlAs HEMT Technology

The effects of the substrate temperature in the molecular beam epitaxy growth of on have been investigated. A strong dependence of the structural, electrical, and optical properties of films on the growth temperature has been found and optimized material can be grown at 530°C. The low substrate temperatures deteriorate the material quality due to insufficient growth kinetics, while the higher temperatures allow the formation of composition inhomogeneities which also deteriorate the structural, optical, and electrical characteristics of . Using buffers grown at 530°C, state‐of‐the‐art high electron mobility transistors were fabricated and showed reduced output conductance and no kink effect in the I(V) characteristics.

Characterization of lattice-matched and strained GaInAs/AlInAs HEMT structures by photoluminescence spectroscopy

Abstract Low-temperature photoluminescence (PL) measurements have been performed in order to characterize In x Ga 1− x As /In 0.52 Al 0.48 As high electron mobility transistor (HEMT) structures with both lattice-matched ( x In =0.53) and strained ( x In =0.60and 0.65) channels. Samples with electron sheet concentration (n s ) between 0.7 and 3.0 × 10 12 cm -2 have been studied. Strong recombination processes involving the first (E1) and second (E2) electron level with the first heavy-hole level (H1) have been observed. In some cases the parity forbidden transition E2H1 was more intense than the fundamental E1H1 due to its more efficient wave function overlap. Thanks to the Fermi edge enhancement mechanism, we have measured the electron Fermi level (E F ) relatively to the bottom of the n = 2 and n = 1 electron subbands. The values of n s have been deduced from PL measurements and are in good agreement with those measured by transport experiments.

Electron density effects in the modulation spectroscopy of strained and lattice‐matched InGaAs/InAlAs/InP high‐electron‐mobility transistor structures

The effects of the channel electron density on the interband optical transitions of strained (x=0.6 and 0.65) and lattice-matched (x=0.53) InxGa1–xAs/In0.52Al0.48As/InP high-electron-mobility transistor structures have been investigated by phototransmittance at room temperature. Analysis of the ground and first excited transitions for low and high densities, respectively, enabled a separate estimation of the electron densities occupying each one of the first two subbands. It was found necessary to include the modulation of the phase-space filling in the analysis of the spectra, especially for the samples with a high electron density, in which case this modulation mechanism becomes dominant.

Temperature dependence of the photoreflectance of strained and lattice-matched InGaAs/InAlAs single quantum wells

Abstract Temperature dependence of photoreflectance spectra is reported for lattice-matched and strained InxGa1−xAs/In0.52Al0.48As (x = 0.53 or 0.60) single quantum wells with different well widths (L = 5 and 25 nm). Several interband transitions have been observed between heavy-hole and light-hole subbands, and conduction subbands at room temperature and at 5 K. Least-squares fits to an Aspnes third derivative functional form yield the energy, broadening parameter, amplitude and phase of the optical transitions. The evolution of the energetic position versus the temperature is fitted using the Varshni semiempirical relationship. A significative modification of the main optical transition E1H1 is evidenced: as the temperature is decreased below 50 K, E1H1 changes from a free to a bound excitonic transition. The energetic positions of four optical transitions in the strained 25 nm quantum well have been compared with the theoretical values obtained by an envelope function model and yield the conduction band offset parameter Qc in the strained InGaAs/InAlAs system with a high accuracy (Qc = 0.73±0.02).

Interface defects and inhomogeneities induced by alloy clustering in InAlAs buffer layers grown on InP

Abstract In this work, InAlAs layers grown on (100) InP by MBE, at temperatures higher than 530°C have been studied by TEM. Our results show that contrast inhomogeneities appear beyond a critical value of the growth temperature, at which they are nonuniformly distributed. When the temperature increases, the inhomogeneities cover all the layer. A correlation between these inhomogeneities and the presence of precipitates at the interface is also presented.

Photo-induced current transient spectroscopy of Al0.48In0.52As semi-insulating layers grown on InP by molecular beam epitaxy

Deep levels in undoped semi-insulating In 0.52 Al 0.48 As layers grown by molecular beam epitaxy on iron-doped InP have been studied by photoluminescence and photo-induced current transient spectroscopy. The effect of the growth temperature T g in the range from 300 o C to 530 o C has been investigated. The results show that low T g causes the material quality to deteriorate and leads to formation of a higher concentration of deep traps. It is shown that optimized material quality can be obtained For InAlAs layers on InP substrates with T g around 530 o C with sufficiently high resistivity, reduced trap density and good structural properties which is appropriate for fabrication of high electron mobility transistors

Optical properties of InGaAs films embedded in plasma etched InP wells

The optical properties of InGaAs films grown in plasma etched InP wells by molecular beam epitaxy have been investigated and compared to the properties of similar films grown on nonpatterned InP substrates. The excitonic features of the photoluminescence spectra were maintained for the selectively grown well films.

Room‐temperature photoreflectance as an efficient tool for study of the crystalline quality of InAlAs layers grown on InP substrates

Photoreflectance and photoluminescence experiments have been performed on molecular beam epitaxy (MBE) grown InAlAs layers lattice matched to InP substrates in order to evaluate the influence of the growth temperature on the crystalline quality of this material. The study of the photoreflectance broadening parameter at room temperature provides the same indication on crystalline quality as the well‐known linewidth broadening of the photoluminescence at cryogenic temperatures. We show that the best material quality is obtained for the MBE growth temperature of 530u2009°C.