Room-temperature operation of AlGaAs/GaAs resonant tunnelling structures grown by metalorganic vapour-phase epitaxy

Reports improvements in resonant tunnelling through AlGaAs/GaAs double barrier quantum wells grown by metalorganic vapour-phase epitaxy. At room temperature peak-to-valley current ratios up to 2.4 and peak current densities of 1.9*10/sup 4/ A/cm/sup 2/ are obtained.<>     

Band gap uniformity and layer stability of HgTe-CdTe superlattices grown by photon-assisted molecular beam epitaxy

Two material properties important to the application of HgTe/CdTe superlattices for device fabrication are band gap uniformity and thermal stability. In this paper, we present the results of an infrared photoluminescence study of (211)B HgTe/CdTe superlattices grown by photon-assisted molecular beam epitaxy which show that cut-off wavelength uniformity can be controlled to a level commensurate with the demands of advanced infrared detector fabrication. Infrared photoluminescence and transmission electron microscopy were also employed to demonstrate that (211)B HgTe/CdTe superlattices are less prone to interdiffusion than previously believed.     

AlGaAs/GaAs JFETs by organo-metallic and molecular beam epitaxy

Normally-off and normally-on AlGaAs/GaAs heterojunction gate GaAs FETs (HJFETs) for high-speed logic applications have been fabricated with molecular beam epitaxy (MBE) and organometallic vapour phase epitaxy (OM-VPE). The best normally-off devices used MBE n-GaAs active layers and OM-VPE gate layers of p+-AlGaAs and p+-GaAs. Saturation currents followed a square law and current scaling constants were the highest on record for HJFETs, greater than 50 ?A/?m-V2.     

Strained AlGaInAs/AlGaAs quantum wells and quantum-well lasersgrown by molecular beam epitaxy

Suitable growth conditions for strained AlGaInAs grown on GaAs substrates by molecular beam epitaxy (MBE) are presented, and strained layer multiple quantum well AlGaInAs lasers grown by MBE are demonstrated. Low-temperature photoluminescence was used to characterize quantum wells grown at different temperatures with different Al, Ga, and In compositions to establish growth parameters     

Magnetotransport of two-dimensional electron gas in Si/SiGe modulation doped structures grown by gas source molecular beam epitaxy

We have characterized two-dimensional electron gases (2DEGs) in Si/SiGe modulation doped structures grown by gas source molecular beam epitaxy. Hall bar structures were fabricated to characterize the structures and magnetotransport measurements were carried out at temperatures down to 0.4 K. Pronounced Shubnikov-de Haas oscillations were observed in the longitudinal magnetoresistance, indicative of high quality 2DEG in the channel. Electron mobilities up to 87,000 cm² V⁻¹ s⁻¹ with sheet densities about 7 × 10¹¹ cm⁻² were obtained at low temperature. Dingle plots of the magnetoresistance vs reciprocal magnetic field were utilized to determine the single-particle relaxation times in order to investigate scattering mechanisms in these structure. The ratio of the transport scattering time derived from electron mobility to the single-particle relaxation time is of the order of 10, indicating that remote impurity scattering is a dominant factor limiting the mobility of our structures. The behaviour of the magnetotransport data is discussed using a model for parallel conduction.     

A comparative study of phase modulation in InGaAsP/InP andGaAs/AlGaAs based p-i-n and p-p-n-n structures

A theoretical study of the phase modulation in InGaAsP/InP and GaAs/AlGaAs double heterostructure waveguides in the p-i-n and p-p-n-n configurations at wavelengths of 1.3 and 1.55 μm. is reported. The carrier-induced effects (plasma, band filling, and many body) and the field-induced effects (linear electrooptic and electro-refractive) are considered to calculate the change in the refractive index. Both structures made of InGaAsP/InP show higher modulation efficiency than the corresponding structures made of GaAs/AlGaAs in almost all the cases considered due to a larger index change in InGaAsP as its bandgap wavelength is closer to both 1.3 and 1.55 μm     

Phase modulation of mid-infrared radiation in double-quantum-well structures under a lateral electric field

The modulation of polarized radiation by GaAs/AlGaAs structures with tunnel-coupled double quantum wells in a strong lateral electric field is studied. The spectra of the variation in the refractive index under a lateral electric field in the vicinity of the intersubband resonance are experimentally investigated.     

Failure mechanisms of AlGaAs/InGaAs pseudomorphic hemt''s: Effects due to hot electrons and modulation of trapped charge

The reliability of AlGaAs/InGaAs pseudomorphic HEMT's has been investigated by means of thermal and hot-electron accelerated tests. Two commercially available devices have been tested, together with prototypes fabricated by a European supplier. Different failure modes have been observed after hot-electron testing, depending on the device type, i.e. (a) increase of drain current, I_D and threshold voltage, |V_T|, which can be attributed either to thermally-activated electron detrapping or to charge compensation by holes generated by impact ionization; (b) decrease of I_D at low drain to source voltages, V_DS, with the development of a kink in the output characteristics due to the generation of deep levels under the gate and subsequent electron trapping. In the former case, (a), hot carriers and/or high temperature storage only modulate the charge present on deep levels, leading to recoverable alterations of device characteristics. In the latter case, (b), the presence of additional deep levels under the gate leads to a permanent degradation. The link between the observed failure modes and the underlying physical mechanism is investigated by means of different techniques, and the main functional effects of the degradation modes are addressed.     

Oxygen incorporation,photoluminescence, and laser performance of AlGaAs grown by organometallic vapor phase epitaxy

Photoluminescence (PL) of separate confinement heterostructure, single quantum well (SCH-SQW) laser material provides a quantitative evaluation of the quality of AIGaAs grown by organometallic vapor phase epitaxy. There is a good correlation between the oxygen level in the quantum well confining layers measured by secondary ion mass spectroscopy, quantum well PL efficiency, and laser threshold current. When oxygen was reduced from 2.0 × 10¹⁸ cm⁻³ to 1.5 × 10¹⁷ cm^-3, the PL intensity increased by a factor of 12, and the threshold current density was improved from 1300 to 240 A/cm² for a 100 × 600 μm device. Oxygen levels were decreased by using a higher growth rate, shorter interface pause time, higher V/III ratio, and an arsine purifier.     

Nonequivalent heterointerfaces in AlGaAs/GaAs double barrier resonant tunnelling diodes grown by metalorganic vapour phase epitaxy

The peak/valley current ratio, of AlGaAs/GaAs double barrier resonant tunnelling diodes at room temperature is found to be very sensitive to the quality of the GaAs/AlGaAs interface, while the AlGaAs/GaAs interface is much less critical.<>     

AlGaAs/GaAs pnp heterojunction bipolar transistor with carbon-doped collector and emitter grown by atomic layer epitaxy

The first AlGaAs/GaAs pnp heterojunction bipolar transistor (HBT) grown entirely by atomic layer epitaxy (ALE) is reported. Carbon was used as the p-type dopant in the emitter and collector. The use of carbon, with its low diffusivity and the potential for very heavy doping, will lead to reduced emitter and collector resistances in a pnp structure. For the devices reported here, a common emitter current gain over 100 was obtained, with good I/V characteristics.<>     

Deep level transient spectroscopy assessment of silicon contamination in AlGaAs layers grown by metalorganic vapor phase epitaxy

A systematic silicon contamination has been detected by deep level transient spectroscopy in undoped and n-type doped (Te, Se, Sn) AlGaAs layers, grown in two different metalorganic vapor phase epitaxy reactors. DX center generation by substitutional donors, with very specific capture and emission thermal barriers (fingerprints), is the key to unambiguously identifying their presence, with detection limits well below the standard secondary ion mass spectroscopy capability. We comment on the potential sources of Si contamination (most common in this epitaxial technique), and on the relevance of such contamination to interpreting correctly experimental data related to the microscopic structure of DX centers.     

Band offsets in Zn 1−x Cd x Te/ZnTe single-quantum-well structures grown by molecular-beam epitaxy on GaAs(001) substrates

ZnTe heteroepitaxial layers and ZnTe/Zn _1?x Cd _x Te/ZnTe strained quantum-confinement structures grown by molecular-beam epitaxy on GaAs(001) were studied by low-temperature cathodoluminescence spectroscopy and current-relaxation deep-level transient spectroscopy (DLTS). A peak related to electron emission from the ground size-quantization level in the conduction-band was observed in the DLTS spectra of quantum-confinement structures. The conduction-band offset parameter Q _C was determined from the DLTS and cathodoluminescence data. For Zn _1?x Cd _x Te/ZnTe single-quantum-well structures with x=0.2–0.22, Q _C equals 0.82 ± 0.05. The effect of internal elastic strain on the band offsets and Q _C at the Cd _x Zn _1?x Te quantum well interfaces was calculated; the results of calculations agree well with experimental data.     

Planar junctions in silicon on oxide grown using lateral epitaxy by seeded solidification

Current-voltage characteristics of large planar junctions fabricated in silicon on oxide have been studied. These junctions have slightly higher reverse leakage currents and slightly lower breakdown voltages than similar junctions fabricated in bulk silicon. The electrical properties of the junctions are dependent on the regrowth parameters of the silicon films. Fairly uniform junction properties are obtained over the entire sample.     

Metalorganic vapor phase epitaxy growth and properties of GaAs/AlGaAs and InGaAs/GaAs quantum well structures on (111)A GaAs substrates

We review the recent advances in the fabrication and properties of GaAs/AlGaAs and InGaAs/GaAs quantum well (QW) structures grown on (111)A GaAs substrates by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE). We show that a 25-period GaAs/AlGaAs multi-QW (MQW) structure was fabricated with good crystal quality, high photoluminescence (PL) emission intensity and monolayer (ML) interfacial roughness. A PL full width at half maximum (FWHM) of 10.5 meV was achieved for a 25-period MQW with a well width of 44 Å. This is the narrowest linewidth reported to date for any similar structures grown on (111)A or B substrates by any growth technique. We also report the properties of an InGaAs/GaAs single quantum well structure grown on (111)A GaAs. For this structure, the PL FWHM value was 9.1 meV, corresponding to a 1 ML interfacial roughness for a well width of 41 Å. This is the first demonstration of an InGaAs/GaAs quantum well structure grown on (111)A or (111)B GaAs by MOVPE.     

Meltback etching and regrowth of GaAs/AlGaAs in liquid phase epitaxy for fabrication of microlens

Meltback etching was performed both on planar and selective areas. In the case of planar etching, we could see the effect of convection. Such a tendency was observed also for selective etching when the degree of undersaturation was large. By varying the mask opening area, composition of the melt, and etching time, a precise control of the etched shape was possible and a hemispherical shape was obtained. Large anisotropic meltback behavior was apparent when the melt contained no aluminium content. But as the added amount of aluminium was increased, the etched shape became circular. Regrowth characteristics showed gallium capturing phenomenon when the amount of supersaturated arsenic was large. By reducing the supersaturated arsenic content, a successful growth could be obtained.     

Defects in mercury-cadmium telluride heteroepitaxial structures grown by molecular-beam epitaxy on silicon substrates

Defects in mercury-cadmium-telluride heteroepitaxial structures (with 0.3 to 0.4 molar fraction of cadmium telluride) grown by molecular-beam epitaxy on silicon substrates are studied. The low-temperature photoluminescence method reveals that there are comparatively deep levels with energies of 50 to 60 meV and shallower levels with energies of 20 to 30 meV in the band gap. Analysis of the temperature dependence of the minority carrier lifetime demonstrates that this lifetime is controlled by energy levels with an energy of ～30 meV. The possible relationship between energy states and crystal-structure defects is discussed.     

Local structures around Er atoms doped in GaAs by low-temperature molecular beam epitaxy

Er-doped GaAs samples were grown by molecular beam epitaxy at 400°C and 590°C. The samples were investigated by photoluminescence (PL) and fluorescence extended X-ray absorption fine structure (EXAFS) measurements in order to find the relationship between the local structures around the Er atoms and the PL properties. Er-related PL peaks were observed only for the samples grown at a low temperature (400°C). The fluorescence EXAFS measurements showed the Er atoms were located on tetrahedral interstitial site when the growth temperature was low. On the other hand, when the growth temperature was high (590°C), the Er atoms substituted the Ga site in GaAs lattice.     

Properties of structures based on laser-plasma Mn-doped GaAs and grown by MOC-hydride epitaxy

A method of doping GaAs with Mn using the laser evaporation of a metal target during MOC-hydride epitaxy is developed. The method is used to form both homogeneously doped GaAs:Mn layers and two-dimensional structures, including a δ-doped GaAs:Mn layer and a In_xGa_1?x As quantum well separated by a GaAs spacer with a thickness of d= 3–6 nm. It is shown that, at room temperature, the formed structures have magnetic and magnetooptical properties most probably caused by the presence of MnAs clusters. In the low-temperature region (～ 30 K), the anomalous Hall effect is observed. This effect is attributed to the exchange interaction between Mn ions via 2D-channel holes.