Growth of the dilute magnetic semiconductor GaMnN by molecular-beam epitaxy

Growth by molecular-beam epitaxy (MBE) of the dilute-magnetic alloy GaMnN is reported. The Mn concentration, as determined by Auger electron spectroscopy (AES), is found to be linear with increasing Mn-cell temperature up to ∼43at.%Mn. No second phases are observed for Mn levels below 9 at.%. The cubic-phase Mn₄N is found to be the thermodynamically stable phase at the growth conditions used to produce GaMnN. Hysteresis in M versus H is observed in both GaMnN and GaMnN:C grown on both sapphire and metal-oxide chemical-vapor deposition (MOCVD) GaN at several growth temperatures. Magnetotransport results show the anomalous Hall effect, negative magnetoresistance, and magnetic hysteresis, indicating that Mn is incorporating into the GaN and forming the ferromagnetic-semiconductor GaMNN. Room-temperature hysteresis is obtained in magnetization measurements with an optimum Mn concentration of ∼3 at.%.     

Silicon implanted super low-noise GaAs MESFET

Super low-nose GaAs MESFETs have been fabricated using direct ion implantation into undoped LEC substrates. Microwave results at 12 GHz include a noise figure of 1.3 dB, with an associated gain of 10.3 dB and a maximum available gain of 14.9 dB.     

Growth temperature dependence of InP nanopyramids grown by selective-area flow rate modulation epitaxy

We have grown InP nanopyramids by selective-area flow rate modulation epitaxy and investigated their structures with a high-resolution scanning electron microscope. The shape of InP nanopyramids strongly depends on growth temperature. At lower growth temperatures, InP forms two horns toward 1 1 1A directions. At higher growth temperatures, there were some thermal pits on {1 1 1}A sidewalls of InP nanopyramids. Furthermore, some droplets were observed on InP nanopyramids. In contrast, {1 1 1}B facets were stable even at high growth temperatures. The behaviors were discussed in relation to a crystallographic model.     

Compound semiconductors for low-noise microwave MESFET applications

In order to determine the low-noise potential of microwave MESFET's fabricated from materials other than GaAs, a one-dimensional FET model is employed. From material parameters and device geometry the model enables the calculation of a small-signal equivalent circuit from which performance information is acquired. Material parameters, as predicted from Monte Carlo calculations, are used to simulate 1-µm devices fabricated from GaAs as well as InP, Ga0.47In0.53As, InP0.8As0.2, Ga0.27In0.73P0.4As0.6, and Ga0.5In0.5As0.96Sb0.04. Results obtained from simulations comparing a Ga0.5In0.5As0.96- Sb0.04device to an equivalent GaAs device indicate that a decrease in minimum noise figure of almost a factor of two is possible. Considerable improvement in noise performance over a GaAs device is also predicted for devices fabricated from Ga0.47In0.53As and Ga0.27In0.73P0.4As0.6. In addition, the quaternary and ternary devices as well as the InP device should exhibit superior gain and high-frequency performance compared to GaAs devices.     

High-resolution x-ray diffraction study of InAs-GaAs superlattices grown by molecular-beam epitaxy at low temperature

InAs-GaAs superlattices grown by molecular-beam epitaxy at low temperature are investigated by high-resolution x-ray diffractometry. It is shown that despite a very high density of point defects due to the presence of excess arsenic, the as-grown superlattice has high crystal perfection. An analysis of the changes in the x-ray diffraction curves shows that high-temperature annealing, which is accompanied by the formation of As clusters and diffusion of indium, produces significant structural transformations in the GaAs matrix and at the interfaces. Fiz. Tekh. Poluprovodn. 32, 24–31 (January 1998)     

Growth of n-Si layers by molecular-beam epitaxy on the substrates heavily doped with boron

Epitaxial n-Si layers doped with phosphorus or erbium have been grown by sublimation molecularbeam epitaxy at 500°C on heavily boron-doped p ⁺-type substrates with resistivity ρ = 0.005 Ω cm. Distribution profiles of the B, Er, and O impurity concentrations in the samples were determined by secondary-ion mass spectrometry. A thermal annealing of the substrate in vacuum at 1300°C for 10 min and growth at a very low substrate temperature made it possible to obtain an extremely abrupt profile for doping impurities at the layer-substrate interface. This method for growth of n-p ⁺ junctions considerably improves their electrical and luminescent characteristics.     

Optical monitoring of technological parameters during molecular-beam epitaxy

It is shown that one can use low-coherence tandem interferometry to measure the substrate temperature during the course of molecular-beam epitaxy in the case of oblique incidence of the probing light onto the surface. The temperature conditions in the Ob??-M installation for growing heteroepitaxial structures of cadmium and mercury tellurides and in the RIBER SIVA-21 installation for the growth of silicon-germanium structures are investigated. Calibration curves relating the readings of the standard thermocouple fixed within the heater to the true substrate temperature in the range 0?C500°C are created.     

Luminescent Si-Ge solid solution layers ER-doped in molecular-beam epitaxy

Erbium-doped Si_1?x Ge_x epitaxial layers have been grown by sublimation molecular-beam epitaxy (SMBE) in an atmosphere of germane (GeH₄). Doping with erbium was done during growth, with single-crystal Si:Er as the source of Er. The Si-Si_1?x Ge_x (0.01≤x≤0.09) interface was studied by secondary-ion mass spectrometry. Er and Ge show concentration profiles with abrupt boundaries and a significant decrease in their surface segregation. This means that hydrogen acts as a “surfactant.” Data on the luminescent properties of the Er-doped Si/Si_1?x Ge_x samples are reported.     

A low-noise dual-gate GaAs MESFET for UHF TV tuner

Demonstrates a new dual-gate GaAs MESFET specially designed for a low-noise UHF TV tuner. The device has been designed under the philosophy as follows: (1) to reduce |S/SUB 11/| and input Q of the field-effect transistor (FET) at the smallest expense of the low-noise feature inherent in GaAs MESFET's (2) to obtain automatic gain control (AGC) and cross-modulation performances compatible with those of a conventional Si MOS tetrode. The optimized pattern geometry satisfying the above philosophy was obtained through theoretical and experimental studies. The FET, of which minimum noise figure (NF) value is as low as 0.9 dB at 1 GHz, was compatible with an Si MOS tetrode in a conventional tuner circuit owing to the small |S/SUB 11/| and low input Q values obtained. The AGC and cross-modulation performance were also satisfactory.     

A low-noise GaAs MESFET made with graded-channel doping profiles

We have demonstrated that devices fabricated from epitaxially grown material with a graded-channel doping profile are capable of improved microwave performance. For operation at 12 GHz, graded-channel doping profile devices have an associated gain that is always 1 dB higher at the minimum noise-figure point compared to ion-implanted Gaussian-channel doping profile devices. A noise figure of 1.60 dB with 11-dB associated gain has been obtained at 12 GHz for 0.5-µm × 300-µm gate devices. A tranconductance of 200 mS/mm for this device has been achieved.     

Dependence of the concentration of ionized donors on epitaxy temperature for Si:Er/Si layers grown by sublimation molecular-beam epitaxy

The dependence of the concentrations of the Er impurity and ionized donors on the epitaxy temperature has been studied before and after annealing of Si:Er/Si layers grown by sublimation molecular-beam epitaxy. n-Si:Er layers have been grown in the temperature range 400–800°C and annealed in hydrogen atmosphere at a temperature of 800°C for 30 min. The possible nature of the donor centers is discussed.     

Long wavelength InGaAs-InGaAlAs-InP diode lasers grown bysolid-source molecular-beam epitaxy

The authors have fabricated InGaAs-InGaAlAs-InP strained quantum well lasers with wavelengths as long as 2208 nm using solid-source molecular-beam epitaxy. A continuous-wave threshold current density of 370 A/cm² at 20°C and characteristic temperature of 53 K have been achieved     

A study of void defects in metalorganic molecular-beam epitaxy grown HgCdTe

Void defects that occur under Hg deficient conditions during the metalorganic molecular beam epitaxy (MOMBE) growth of HgCdTe have been characterized using secondary electron microscopy (SEM) and energy dispersion spectrometry (EDS) mapping as well as by EDS quantitative analysis. For a set of HgCdTe samples grown under a range of Hg fluxes, it was found that the surface morphology had a significant dependence on the Hg flux. An optimum growth window defined by a narrow range of Hg fluxes was identified in which there exists a smooth surface with few voids, whereas at either side of the Hg window surfaces were rough. This surface morphology correlated very well with a minimum in the x-ray line widths and maximum hole concentration and mobility values. This correlation is important for the growth of HgCdTe materials and subsequent device fabrication. Several types of void morphologies have been observed with different correlation to Te and Hg. It was found that there is a pronounced Te enrichment and Hg deficiency associated with most of the developed voids, as compared to the composition of the HgCdTe films. It was also found that most of the voids originated within the HgCdTe film. A mechanism for void formation and growth is proposed. In addition, it was found that annealing caused the voids to separate from the HgCdTe film.     

Effect of the arsenic cracking zone temperature on the efficiency of arsenic incorporation in CdHgTe films in molecular-beam epitaxy

Cd _x Hg_{1 ? x} Te films with x ≈ 0.22 and thickness of ～10 µm have been grown by molecular-beam epitaxy on gallium arsenide substrates and doped in situ with arsenic. Activation annealing of doped films provided p-type conduction with a hole density of up to 10¹⁷ cm^?3. The influence exerted by the arsenic cracking zone temperature on the efficiency of arsenic incorporation into the CdHgTe film was studied. A model describing the dependence of the arsenic concentration in the films on the arsenic cracking zone temperature was suggested. A comparison of the model and the experimental data demonstrated that the incorporation efficiency of diatomic arsenic is approximately two orders of magnitude higher than that of tetratomic arsenic.     

Arsenic cluster superlattice in gallium arsenide grown by low-temperature molecular-beam epitaxy

Molecular-beam epitaxy at 200 °C is used to grow an InAs/GaAs superlattice containing 30 InAs delta-layers with a nominal thickness of 1 monolayer, separated by GaAs layers of thickness 30 nm. It is found that the excess arsenic concentration in such a superlattice is 0.9×10²⁰ cm⁻³. Annealing the samples at 500 and 600 °C for 15 min leads to precipitation of the excess arsenic mainly into the InAs delta-layers. As a result, a superlattice of two-dimensional sheets of nanoscale arsenic clusters, which coincides with the superlattice of the InAs delta-layers in the GaAs matrix, is obtained. Fiz. Tekh. Poluprovodn. 32, 1161–1164 (October 1998)     

Measurements of parameters of the low-temperature molecular-beam epitaxy of GaAs

Phase diagrams of GaAs (001) surface structures were used to calibrate sensors of the substrate temperature and As flux in molecular-beam epitaxy systems. The sublimation temperature of amorphous layers of As adsorbed on GaAs was measured. It was shown that this temperature is constant and does not depend on the rate of substrate heating, layer thickness, or the degree of vacuum in the system. The sublimation temperature of amorphous As can be used as a reference point to calibrate the substrate temperature in the range of low growth temperatures.     

Effect of the annealing temperature on the low-temperature photoluminescence in Si:Er light-emitting structures grown by molecular-beam epitaxy

The photoluminescence spectra of light-emitting structures based on silicon doped with erbium during the course of molecular-beam epitaxy at a temperature of 500°C are studied at 4.2 K on being annealed at 800–900°C. Three sets of lines belonging to the emitting centers of erbium in silicon with a low oxygen-impurity concentration are revealed.     

Features of molecular-beam epitaxy and structural properties of AlInSb-based heterostructures

AlInSb layers are grown on highly lattice-mismatched GaAs (100) substrates by molecular-beam epitaxy (MBE) and studied in situ by reflection high-energy electron diffraction and ex situ by scanning and transmission electron microscopy (SEM and TEM). It is shown that one feature of AlInSb/GaAs heterostructure features is a high probability of forming microtwins; methods for decreasing their concentration are proposed. To initiate AlInSb growth on GaAs substrates under high lattice-mismatch (∼14.5%) conditions and to stimulate the transition to 2D growth, the GaAs layer surface was preliminarily exposed to an antimony flux followed by deposition of an intermediate AlSb buffer layer. The optimization of initial MBE growth stages of Sb-containing layers on the GaAs surface allows a decrease in the defect density in the GaAs/AlInSb heterostructures more than by two orders of magnitude, including a drastic decrease in the microtwin density. Optimal MBE growth conditions for Al _x Al_{1 − x} Sb are determined in a wide composition range (0 < x < 0.3). The TEM and SEM studies confirm the high structural quality of grown GaAs/AlInSb heterostructures. Hall-effect measurements showed the dependence of the carrier mobility and concentration on the aluminum content in AlInSb layers and allowed preliminary conclusions on scattering mechanisms.