K. Alavi

Measurement of the conduction‐band discontinuity of molecular beam epitaxial grown In0.52Al0.48As/In0.53Ga0.47As, N‐n heterojunction by C‐V profiling

We report the first measurement of the conduction‐band discontinuity ΔEc for molecular beam epitaxial grown N‐n In0.52Al0.48As/In0.53Ga0.47As heterojunction using the C‐V profiling technique outlined by Kroemer et al. We find ΔEc=(0.50±0.05) eV @297 K corresponding to (71±7)% ΔEg. An interface charge density σi of (4.0±0.8)×1011 cm−2 was also obtained. A knowledge of ΔEc is of importance for quantifying carrier confinement in double heterostructure lasers fabricated from these ternary compounds.

1.5–1.6‐μm Ga0.47In0.53As/Al0.48In0.52As multiquantum well lasers grown by molecular beam epitaxy

The first successful preparation of optically pumped and current injection Ga0.47In0.53As/Al0.48 In0.42As multiquantum well lasers is reported. These devices, operating at room temperature in the 1.5–1.6‐μm range, have been prepared by molecular beam epitaxy with well thicknesses as low as 80–90 A and barrier thicknesses as low as 30 A. In the broad area devices with a total active layer thickness of 0.14 μm we have observed threshold current density as low as 2.4 kA/cm2.

Photovoltaic quantum well infrared detector

A photovoltaic infrared detector based on photoemission from a single modulation doped GaAs‐AlGaAs quantum well is presented. The modulation doping provides a built‐in field which allows unbiased operation. We show results from a device which is sensitive to 180 meV (7 μm wavelength) light, with a bandwidth of 20 meV, for which we estimate the quantum efficiency to be 1%. We demonstrate that the detector may be tuned to different wavelengths by varying the width of the well.

High-gain Al 0.48 In 0.52 As/Ga 0.53 As vertical n-p-n heterojunction bipolar transistors grown by molecular-beam epitaxy

We report the first vertical n-p-n heterojunction bipolar transistors formed in the (Al,In)As/(Ga,In)As alloy system. The structures grown by molecular-beam epitaxy (MBE) use a wide band-gap (Eg = 1.44 eV) Al0.48In0.52As emitter on a lower band gap (Eg = 0.73 eV) Ga0.47In0.53As base 2500 Å in width. Transistors with both abrupt and graded heterojunction emitters were demonstrated with dc current gains of 140 and 280, respectively, at a collector current of 15 mA. The (Al,In)As/(Ga,In)As heterojunction transistors offer the attractive possibility of optical integration with long wavelength lasers and photodetectors.

Lateral refractive index step in GaAs/AlGaAs multiple quantum well waveguides fabricated by impurity‐induced disordering

The lateral refractive index step Δn in GaAs/AlGaAs multiple quantum well waveguides fabricated by impurity‐induced disordering is determined. Δn is found to depend on polarization and wavelength, increasing towards the active‐layer band gap. The lateral index step can be as large as 4×10−2 for a Zn disordered waveguide device at 875 nm. A strong birefringence of the waveguiding characteristics is observed leading to an antiguiding behavior of TM‐polarized light for wavelengths sufficiently below the band gap.

Grating enhancement of quantum well detector response

We have measured the enhancement in the response of a quantum well infrared detector by the incorporation of a metallic diffraction grating into the structure. We find an enhancement ratio of about 30, and its spectrum indicates that waveguiding of diffracted light occurs within the sample. Strong coupling to evanescent modes of the grating is not observed.

Experimental determination of the edge depletion width of ahe two‐dimensional electron gas in GaAs/AlxGa1−xAs

A new method based on one‐dimensional localization theory is introduced to determine the width of the two‐dimensional electron gas (2DEG) in narrow conducting channels of GaAs/AlxGa1−xAs heterojunctions. The edge depletion width of the 2DEG, measured by the difference between this width and the metallurgical width of the channel, is ∼0.5 μm±0.2 μm for a 2DEG density ns=1.5×1011/cm2.

In 0.53 Ga 0.47 As FET's with insulator-assisted Schottky gates

Schottky-gate FETs have been fabricated on n-type In<inf>0.53</inf>Ga<inf>0.47</inf>As using a thin interfacial silicon nitride layer between the metal and the epitaxial layer to reduce the gate leakage current. In<inf>0.53</inf>Ga<inf>0.47</inf>As was grown by molecular beam epitaxy on semi-insulating InP substrates and silicon nitride was grown by plasma-enhanced chemical vapor deposition. Devices with 1.2µm gate length and net donor doping in the mid 10¹⁶cm^-3range show dc transconductance of up to 130mS/mm. Both depletion and enhancement mode operation were observed. The effective saturation velocity of electrons in the channel is deduced to be 2.0 ± 0.5 × 10⁷cm/sec, a value 60 to 70% higher than that in GaAs MESFETs. The insulator-assisted gate technology has many advantages in fabrication flexibility and control compared with other approaches to realizing high-speed microwave and logic in FETs in In<inf>0.53</inf>Ga<inf>0.47</inf>As.

Well size related limitations on maximum electroabsorption in GaAs/AlGaAs multiple quantum well structures

Experimentally determined maximum electroabsorption in GaAs/Al0.33Ga0.67As multiple quantum wells over the quantum well width range of 17–260 A is related to the confinement of the electronic wave functions in the quantum well, increasing with enhanced confinement. However, for very narrow wells, this increase in maximum electroabsorption is diminished by strong broadening of the excitonic resonances due to phonon scattering, eventually leading to a peak value of 22 200 cm−1 at a 35 A well width.

Optically pumped 1.55‐μm double heterostructure GaxAlyIn1−x−yAs/AluIn1−uAs lasers grown by molecular beam epitaxy

We report the first successful realization of room‐temperature laser action at a wavelength of 1.55 μm in a new double heterostructure in which the active layer of GaxAlyIn1−x−yAs is confined between two cladding layers of AluIn1−uAs. The structure was grown on InP by molecular beam epitaxy, and was pumped optically by a Q‐switched yttrium aluminum garnet laser. Peak output power of up to 5 W was obtained at an incident power corresponding to four times that required for threshold without catastrophic degradation. Temperature dependence of the threshold power can be characterized by Pth∼exp(T/T0) with T0=60 °C for 20 °C≤T≤100 °C.