Effect of isovalent doping with phosphorus on the cluster formation in gallium arsenide grown by molecular-beam epitaxy at a relatively low temperature

Transmitting electron microscopy and X-ray diffractometry are used to study the GaAs layers undoped or doped uniformly with phosphorus (2.3 mol %) and grown at a temperature of 250°C and then annealed isochronously at 400, 500, 600, or 700°C. It is ascertained that doping with phosphorus reduces the amount of excess arsenic captured in the layer in the course of growth and also brings about a retardation of precipitation during subsequent annealing. The concentration of excess arsenic in undoped samples amounted to ～0.2 at %; clusters were observed after annealing at a temperature of 500°C. The concentration of excess arsenic amounted to 0.1 at % in the samples containing phosphorus; in this case, the clusters were observed only after a heat treatment at 600°C. The average size of clusters in doped samples is smaller than that in undoped samples at the same heat-treatment temperatures.     

Effect of isovalent indium doping on excess arsenic in gallium arsenide grown by molecular-beam epitaxy at low temperatures

X-ray spectral microanalysis, optical transmission measurements at near-infrared wavelengths, and x-ray diffractometry are used to show that the isovalent indium doping of gallium arsenide during molecular-beam epitaxy at low temperatures leads to an increase in the concentration of excess arsenic trapped in the growing layer. Fiz. Tekh. Poluprovodn. 32, 778–781 (July 1998)     

Structure and properties of InGaAs layers grown by low-temperature molecular-beam epitaxy

This paper describes studies of InGaAs layers grown by molecular-beam epitaxy on InP (100) substrates at temperatures of 150–480 °C using various arsenic fluxes. It was found that lowering the epitaxy temperature leads to changes in the growth surface, trapping of excess arsenic, and an increased lattice parameter of the epitaxial layer. When these lowtemperature (LT) grown samples are annealed, the lattice parameter relaxes and excess arsenic clusters form in the InGaAs matrix. For samples grown at 150 °C and annealed at 500 °C, the concentration of these clusters was ∼8×10¹⁶ cm⁻³, with an average cluster size of ∼5 nm. Assuming that all the excess arsenic is initially trapped in the form of antisite defects, the magnitude of the LT-grown InGaAs lattice parameter relaxation caused by annealing implies an excess arsenic concentration (N _As−N _Ga−N _In)/(N _As+N _Ga+N _In)=0.4 at.%. For layers of InGaAs grown at 150 °C, a high concentration of free electrons (∼1×10¹⁷ cm⁻³) is characteristic. Annealing such layers at 500 °C decreases the concentration of electrons to ∼1×10¹⁷ cm⁻³. The results obtained here indicate that this change in the free-electron concentration correlates qualitatively with the change in excess arsenic concentration in the layers. Fiz. Tekh. Poluprovodn. 33, 900–906 (August 1999)     

Influence of indium doping on the formation of silicon-(gallium vacancy) complexes in gallium arsenide grown by molecular-beam epitaxy at low temperatures

Low-temperature photoluminescence (PL) studies of gallium-arsenide layers grown by molecular-beam epitaxy at low (200 °C) temperatures (LT GaAs) and doped with silicon or a combination of silicon and indium have been performed. The PL spectra of as-grown samples reveal a shallow acceptor-based line only. After annealing, an additional line at ∼1.2 eV appears, which is attributable to Si_Ga-V _Ga complexes. The activation energy of complex formation is found to be close to the activation energy of migration of gallium vacancies and is equal to 1.9±0.3 eV for LT GaAs: Si. It is found that doping with a combination of silicon and indium leads to an increase in the activation energy of formation of Si_Ga-V _Ga complexes to 2.5±0.3 eV. We believe that this increase in the activation energy is controlled by the gallium vacancy-indium interaction through local lattice deformations. Fiz. Tekh. Poluprovodn. 33, 1187–1191 (October 1999)     

Properties of manganese-doped gallium arsenide layers grown by liquid-phase epitaxy from a bismuth melt

The electrical and photoluminescence properties of p-GaAs: Mn(100) layers grown by liquid-phase epitaxy from a bismuth solvent at various temperatures are investigated. It is shown that such layers have a low concentration of background impurities and a low degree of electrical compensation up to a hole concentration of p=1×10¹⁸ cm⁻³ at 295 K. As the concentration of manganese in the liquid phase increases, the concentration of donors in the GaAs: Mn layers increases superlinearly, while the concentration of ionized acceptors increases sublinearly. This leads to an increase in the compensation factor. The donor and acceptor concentrations, as well as the degree of compensation, increase more slowly with increasing temperature. Reasons for the donor compensation are discussed from a crystal-chemical point of view, and it is shown that the preassociation of manganese and arsenic atoms in the liquid phase could be responsible for generating these compensated donors. It is postulated that the compensating donors are nonradiative recombination centers, whose concentration increases with increasing doping level more rapidly than does the concentration of Mn_Ga acceptors. Fiz. Tekh. Poluprovodn. 32, 791–798 (July 1998)     

Controlled oxygen incorporation in indium gallium arsenide and indium phosphide grown by metalorganic vapor phase epitaxy

The defect engineering in metalorganic vapor phase epitaxy In_xGa_1-xAs and InP by controlled oxygen doping using diethyl aluminum ethoxide (DEALO) was developed in this study. DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in In_xGa_1−xAs: Si with 0 ≤ x ≤ 0.25. With the same DEALO mole fraction during growth, the incorporation of Al and O was found to be independent of x, but the compensation of Si donors decreases with increasing In content. Deep level transient spectroscopy analysis on a series of In_xGa_1-xAs: Si. samples with 0 ≤ x ≤ 0.18 revealed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. As the In composition was increased, one or more of these deep levels became resonant with the conduction band and led to a high electron concentration in oxygen doped In_0.53Ga_0.47As. Low temperature photoluminescence emission measurements at 12K on the same set of samples revealed the quenching of the near-band edge peak, and the appearance of new oxygen-induced emission features. DEALO doping in InP has also led to the incorporation of Al and O, and the compensation of Si donors due to oxygen-induced multiple deep levels.     

Indium gallium arsenide antimonide photodetector grown by liquid phase epitaxy: Electrical characterization and optical response

Current–voltage (I–V) and R₀A curves and spectral response as a function of bias voltage and temperature of p–n indium gallium arsenide antimonide (In_0.14Ga_0.86As_0.13Sb_0.87)/n-GaSb photodiodes are presented. InGaAsSb quaternary alloys with a bandgap energy of about 653 meV were grown using the liquid phase epitaxy technique on top of (100) GaSb substrates. Device structure was fabricated using a process that includes passivation with sodium sulfide, thermal annealing and metallizations. The diode architecture was a back-illuminated (B-I) structure with a ring-shaped metallic contact in the GaSb substrate face. Photodiode spectral response showed good performance in the entire temperature range between 20 K and 300 K.     

A study of recombination centers related to As-Sb nanoclusters in low-temperature grown gallium arsenide

Electronic traps in “low-temperature” GaAs (LT-GaAs) grown at 150°C were studied. The As-Sb clusters appearing in this material after annealing were located in a plane that contained a single Sb monolayer formed during growth. The diameter of the clusters was as large as 20 nm. For the purpose of measurement, Au-n-GaAs Schottky barriers were used, in which, for certain bias voltages, the space charge region enclosed the narrow LT-GaAs layer containing the plane of clusters. The bias-voltage dependence of the structure capacitance indicates that the majority of the electrons in this layer are captured by traps, whose energy level lies ～0.5 eV below the bottom of the conduction band. The energy density of states at this energy is 10¹⁴ cm^?2 eV^?1, which sharply decreases towards the midgap. The existence of traps with activation energies of ～0.5 eV for the thermal emission of electrons is confirmed by deep-level transient spectroscopy. The magnitude of the electroncapture cross section determined by this method is in the range 5 × 10^?14?1 × 10^?12 cm². It is assumed that traps of this type are related to large As-Sb clusters.     

p+?n hyperabrupt GaAs varactors grown by molecular-beam epitaxy

Gallium-arsenide p?n junction hyperabrupt varactor diodes have been grown by molecular-beam epitaxy. Near the junction the donor profile at depth x tracked x?1.2. A capacitance ratio C0/C12 of 10 is observed for bias voltages of 0 and 12 V.     

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.     

Enhanced radiative recombination in AlGaN quantum wells grown by molecular-beam epitaxy

Dependences of the intensity of cathodoluminescence in multiple Al_0.55Ga_0.45N/Al_0.45Ga_0.55N quantum wells grown by molecular-beam epitaxy on the growth conditions are studied. An increase (by almost two orders of magnitude) in the intensity of the cathodoluminescence peak with an energy of 4.45 eV is observed as the quantum-well layer grows in the conditions of deep depletion with respect to ammonia. In this case, a tendency towards the mode of three-dimensional growth can be inferred from the pattern of diffraction of high-energy electrons; this effect is interpreted using a model of formation of AlGaN quantum dots.     

Phase separation in Ga-doped MgZnO layers grown by plasma-assisted molecular-beam epitaxy

We report on the phase separation of Ga-doped MgZnO layers grown by plasma-assisted molecular-beam epitaxy. Based on X-ray diffraction, low-temperature (10 K) photoluminescence, and reflection high-energy electron diffraction observations, it is possible to classify the phase of Ga-doped MgZnO layers into three regions depending on the incorporated Ga concentration ([Ga]). Single-phase Mg_0.1Zn_0.9O layers are grown when [Ga] is less than 1×10¹⁸ cm⁻³. For [Ga] between 1×10¹⁸ cm⁻³ and 1×10²⁰ cm⁻³, ZnO and Mg_0.2Zn_0.8O coexist, where electron transport is considered to be via two-channel conduction. When [Ga] exceeds 1×10²⁰ cm⁻³, the Ga-doped MgZnO layers become polycrystalline, where carrier compensation takes place presumably due to grain boundaries.     

Schottky barriers on p-type gallium arsenide prepared by molecular beam epitaxy

Rectifying contacts have been made by depositing epitaxial films of aluminium and antimony on p-type gallium arsenide by molecular beam epitaxy. The I/V and C/V characteristics were almost ideal. The barrier heights determined from the 1/V characteristics were 0.64 eV for aluminium and 0.66 eV for antimony. The significance of these results is briefly discussed.     

Superlattice optical-cavity multiple-quantum-well (SOC-MQW) lasers grown by molecular-beam epitaxy

A new-structure multiple-quantum-well laser utilising superlattice waveguides and superlattice barriers is proposed and fabricated by molecular-beam epitaxy using GaAs/AlGaAs. Room-temperature CW operation with a threshold current of 40 mA and external differential quantum efficiency per facet of 20% is demonstrated.     

Effect of ambient on photoluminescence from GaN grown by molecular-beam epitaxy

We report the investigation of reversible-transient effects in photoluminescence (PL) of GaN layers in different measurement ambients including air, oxygen, nitrogen, and hydrogen. While the presence of air and oxygen led to similar amounts of significant decrease in overall luminescence, nitrogen and hydrogen produced a much smaller effect. Data on the different behaviors of the near-band-edge and the deep-level (yellow luminescence (YL)) spectral components of the luminescence with change from vacuum to the various ambient gases will be presented. A redshift of the deep-level luminescence band was noticed in oxygen or air ambient that has been attributed to a decrease of the band bending.     

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     

Luminescence study of ZnTe:Cr epilayers grown by molecular-beam epitaxy

Incorporation of Cr into ZnTe epilayers grown by molecular-beam epitaxy (MBE) is reported. Photoluminescence (PL) using both continuous wave (CW) and pulsed-excitation sources is used to characterize the radiative efficiency of doped layers in the infrared region. The Cr²⁺ ions produce a broad emission band peaking in the 2–3 μm range, which is of potential use in tunable-laser devices. The optimum Cr concentration for achieving bright, room-temperature infrared emission was found to be in the range from low- to mid-10¹⁸ cm⁻³. Temperature-dependent luminescence studies were performed to determine thermal-quenching activation energies. Using a pulsed-laser operating at 1.9 μm, an investigation of emission lifetimes was made. The emission-decay curves for the Cr²⁺ recombination in ZnTe:Cr films could be described by a single exponential and were nearly independent of temperature from 80 K to 300 K. A room-temperature lifetime of ∼2.5 μsec in a ZnTe:Cr layer with [Cr] ∼1.4 × 10¹⁸ cm⁻³ compares favorably with values reported for bulk ZnTe:Cr.     

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.     

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.