Influence of intrinsic point defects on the formation of structural defects and optically active centers during the annealing of erbium-and dysprosium-implanted silicon

The photoluminescence spectra and behavior of the structural defects in layers obtained by implanting 1.0–1.8-MeV Er and Dy ions at a dose of 1×10¹³ cm⁻² are investigated after annealing at 1000–1200 °C for 0.5–1 h in argon or a chlorine-containing atmosphere. The structural defects are studied using transmission electron microscopy and selective chemical etching. The dominant features in the luminescence spectra of the Si:Er and Si:Dy layers following annealing in the chlorine-containing atmosphere are lines associated with the formation of edge dislocations, while the dominant features following the annealing of Si:Er and Si:Dy layers in argon are the erbium-related lines. A comparative analysis of the luminescence spectra of the Si:Er and Si:Dy layers shows that the highest intensity of dislocation-related luminescence is achieved in the erbium-implanted structures. A significant influence of intrinsic point defects on the structural and optical properties of erbium-and dysprosium-implanted silicon is revealed. Fiz. Tekh. Poluprovodn. 33, 656–659 (June 1999)     

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)     

A study of chemical beam epitaxy of GaAs using tris-dimethylaminoarsenic

The growth of GaAs by chemical beam epitaxy using triethylgallium and trisdimethylaminoarsenic has been studied. Reflection high-energy electron diffraction (RHEED) measurements were used to investigate the growth behavior of GaAs over a wide temperature range of 300–550°C. Both group III- and group Vinduced RHEED intensity oscillations were observed, and actual V/III incorporation ratios on the substrate surface were established. Thick GaAs epitaxial layers (2–3 μm) were grown at different substrate temperatures and V/III ratios, and were characterized by the standard van der Pauw-Hall effect measurement and secondary ion mass spectroscopy analysis. The samples grown at substrate temperatures above 490°C showed n-type conduction, while those grown at substrate temperatures below 480°C showed p-type conduction. At a substrate temperature between 490 and 510°C and a V/III ratio of about 1.6, the unintentional doping concentration is n ∼2 × 10¹⁵ cm⁻³ with an electron mobility of 5700 cm²/V·s at 300K and 40000 cm²/V·s at 77K.     

High purity InxGa1−xSb single crystals with cutoff wavelength of 7–8 µm grown by melt epitaxy

For the first time, InGaSb single crystals with a cutoff wavelength of 7–8 μm were successfully grown on GaAs substrates by a new growth technique named melt epitaxy. The band gap of InGaSb layers obviously narrowed compared with those with the same compositions grown by ordinary methods and the longest cutoff wavelength reached 8.3 μm. High electron mobility of 8.05×10⁴ cm²/Vs and low carrier density of 1×10¹⁵ cm⁻³ at 77 K were obtained indicating high purity of InGaSb epilayers.     

Effect of annealing on the optical and structural properties of GaN:Er

The effect of annealing on the optical and structural properties of gallium nitride layers grown by metalorganic chemical vapor deposition and implanted with 0.8 to 2.0-MeV erbium ions at doses of (1−4)×10¹⁴ cm⁻² is investigated. Additional implantation of 0.11 to 0.28-MeV oxygen ions at doses of (1−4)×10¹⁵ cm⁻² is performed on some samples. Measurements of the Rutherford backscattering of protons show that amorphization of the gallium nitride layers does not occur at the erbium implantation doses investigated. The formation of erbium-related luminescence centers which emit at 1.54 μm ends before the defect structure of the implanted layers is restored during a postimplantation anneal in the temperature range 700–1300 °C. Fiz. Tekh. Poluprovodn. 33, 674–676 (June 1999)     

Electrical characteristics and structural properties of ohmic contacts to p-type 4H-SiC epitaxial layers

Epitaxial films grown by low-temperature liquid phase epitaxy on p-type 4H-SiC were used as strongly doped subcontact layers for making low-resistance contacts to the p-type material. The layers had a bulk resistivity of ∼0.02 Ω · cm and an aluminum atom concentration of ∼1.5×10²⁰ cm⁻³. The absence of polytype inclusions and the distinct crystalline quality of the strongly doped subcontact layers was confirmed by x-ray diffraction methods. Ohmic contacts with resistivities less than 10⁻⁴ Ω · cm² were prepared by depositing and then annealing multilayer metal mixtures containing Al and Ti. The structural properties and energy characteristics of the resulting ohmic contacts are discussed. Fiz. Tekh. Poluprovodn. 33, 1334–1339 (November 1999)     

Experimental study of the transverse Ettingshausen-Nernst effect and thermoelectric power in the presence of a large temperature gradient

The transverse Ettingshausen-Nernst effect and the thermoelectric power of compensated germanium with electron density n=2×10¹¹ cm⁻³ are investigated as a function of the temperature gradient in the range 2−1.5×10³ K·cm⁻¹ at average temperature 350 K. It is shown that the mechanism of charge-carrier scattering does not depend on the temperature gradient, while the Benedick thermoelectric power is due to heating of the current carriers by the heat field. Fiz. Tekh. Poluprovodn. 32, 1313–1314 (November 1998)     

Low oxygen and carbon incorporation in AIGaAs using tritertiarybutylaluminum in organometallic vapor phase epitaxy

High-quality AIGaAs epilayers have been grown by low pressure organometallic vapor phase epitaxy with a new aluminum precursor tritertiarybutylaluminum (TTBAl). Layers grown at 650°C have a featureless mirror surface morphology and strong room temperature photoluminescence. Carbon was not detectable in chemical analysis by secondary ion mass spectroscopy, nor in low temperature (4K) photoluminescence spectra. Oxygen concentration in Al_0.25Ga_0.75As is as low as ∼2−3 × 10¹⁷ cm⁻³. Nominally undoped AIGaAs layers exhibit n-type conductiv-ity with electron concentrations at ∼ 1−1.5 × 10¹⁶ cm⁻³. A high degree of compo-sitional uniformity over 5 cm diam substrates (0.268 ±0.001) was obtained. These results indicate the potential for TTBA1 as an aluminum precursor for low temperature growth of Al-containing III-V alloys.     

Low-temperature photoluminescence in holmium-doped silicon

In this paper the photoluminescence (PL) of holmium-doped silicon is discussed. The silicon was first implanted with holmium ions at energies of 1–2 MeV and doses of 1×10¹³–3×10¹⁴ cm⁻², and then annealed at temperatures of 620–900 °C for 0.5–1 h. In order to increase the concentration of electrically and optically active centers, the silicon was implanted a second time with oxygen ions at energies of 0.14–0.29 MeV and doses of 1×10¹⁴–3×10¹⁵ cm⁻². Several photoluminescence lines, which are attributable to the transitions of electrons from the first excited state of the Ho³⁺ ion (⁵ I ₇) to the ground state (⁵ I ₈), were observed. The amplitudes of the most intense lines, which correspond to transitions at frequencies 5119 and 5103 cm⁻¹, decreased by more than an order of magnitude in the temperature range 4.2−78 K. The PL intensity of the holmium ions increased with increasing concentrations of the implanted rare-earth ions and oxygen. Fiz. Tekh. Poluprovodn. 33, 420–422 (April 1999)     

The effect of neutron irradiation and annealing temperature on the electrical properties and lattice constant of epitaxial gallium nitride layers

Effect of irradiation with high reactor-neutron fluences (Φ = 1.5 × 10¹⁷-8 × 10¹⁹ cm⁻²) and subsequent heat treatments in the temperature range 100–1000°C on the electrical properties and lattice constant of epitaxial GaN layers grown on an Al₂O₃ substrate is considered. It is shown that, with the neutron fluence increasing to (1–2) × 10¹⁸ cm⁻², the resistivity of the material grows to values of about 10¹⁰ Ω cm because of the formation of radiation defects, and, with the fluence raised further, the resistivity passes through a maximum and then decreases to 2 × 10⁶ Ω cm at 300 K, which is accounted for by the appearance of a hopping conductivity via deep defects in the overlapping outer parts of disordered regions. With the neutron fluence raised to 8 × 10¹⁹ cm⁻², the lattice constant c increases by 0.38% at a nearly unchanged parameter a. Heat treatment of irradiated samples at temperatures as high as 1000°C does not fully restore the lattice constant and the electrical parameters of the material.     

P- and N-type doping of GaN and AlGaN epitaxial layers grown by metalorganic chemical vapor deposition

Mg- and Si-doped GaN and AlGaN films were grown by metalorganic chemical vapor deposition and characterized by room-temperature photoluminescence and Hall-effect measurements. We show that the p-type carrier concentration resulting from Mg incorporation in GaN:Mg films exhibits a nonlinear dependence both on growth temperature and growth pressure. For GaN and AlGaN, n-type doping due to Si incorporation was found to be a linear function of the silane molar flow. Mg-doped GaN layers with 300K hole concentrations p ∼2×10¹⁸ cm⁻³ and Si-doped GaN films with electron concentrations n∼1×10¹⁹ cm⁻³ have been grown. N-type Al_0.10Ga_0.90N:Si films with resistivities as low as p ∼6.6×10⁻³ Ω-cm have been measured.     

Indium layers in low-temperature gallium arsenide: Structure and how it changes under annealing in the temperature range 500–700 °C

Transmission electron microscopy is used to study the microstructure of indium δ layers in GaAs(001) grown by molecular beam epitaxy at low temperature (200 °C). This material, referred to as LT-GaAs, contains a high concentration (≈10²⁰ cm⁻³) of point defects. It is established that when the material is δ-doped with indium to levels equivalent to 0.5 or 1 monolayer (ML), the roughness of the growth surface leads to the formation of InAs islands with characteristic lateral dimensions <10 nm, which are distributed primarily within four adjacent atomic layers, i.e., the thickness of the indium-containing layer is 1.12 nm. Subsequent annealing, even at relatively low temperatures, leads to significant broadening of the indium-containing layers due to the interdiffusion of In and Ga, which is enhanced by the presence of a high concentration of point defects, particularly V _Ga, in LT-GaAs. By measuring the thickness of indium-containing layers annealed at various temperatures, the interdiffusion coefficient is determined to be D _In-Ga=5.1×10⁻¹² exp(−1.08 eV/kT) cm²/s, which is more than an order of magnitude larger than D _In-Ga for stoichiometric GaAs at 700 °C. Fiz. Tekh. Poluprovodn. 32, 769–774 (July 1998)     

Variable temperature hall effect on p-Hg1−xCdxTe grown on CdTe and sapphire substrates by liquid phase epitaxy

Variable temperature Hall effect measurements have been made down to 9–10K on p-type Hg_1−xCd_xTe grown by liquid phase epitaxy on both CdTe and sapphire substrates. Carrier freeze-out was usually observed throughout the measured temperature range. For most samples, the hole mobility was well-behaved and exhibited a maximum at ˜ 35K. Values of acceptor ionization energy E_A and donor concentration N_D were estimated from the data, using a model assuming significant compensation, which provided a good fit to the low temperature data. In addition, values of N_D were also estimated from an analysis of the low temperature mobility using the hole effective mass as a parameter to provide reasonable agreement between the N_D values calculated from the Hall coefficient and mobility data. The measured carrier concentration is a result of close compensation between stoichiometric acceptors and donors, with N_D usually in the low-10¹⁷ cm⁻³ range. Average values of E_A for as-grown, undoped x = 0.32 layers on CdTe and sapphire substrates are 7.4 and 6.6 meV, respectively. An activation energy of 0.84 meV was determined for a Cu-doped x = 0.32 layer that was annealed in Hg vapor to reduce the number of Hg vacancies. The average E_A for undoped Hg-annealed x = 0.22 layers on CdTe substrates is 2.35 meV. Layers with x = 0.32 grown on sapphire substrates have average carrier concentrations of 2.92 (σ = 0.54) × 10¹⁶ cm⁻³, compared with 4.64 (θ = 1.26) × 10¹⁶ cm⁻³ for the same composition layers grown on CdTe substrates.     

Radiation hardness of porous silicon

The effect of irradiation by 300-keV Ar⁺ ions on the properties of electrochemically produced porous silicon is studied at doses of 5×10¹⁴–1×10¹⁶ cm⁻². Raman scattering and photoluminescence data are used to show that the radiation hardness of porous silicon layers is substantially greater than that of single crystal silicon. Fiz. Tekh. Poluprovodn. 31, 1126–1129 (September 1997)     

Gadolinium-doped InGaAsSb solid solutions on an InAs substrate for light-emitting diodes operating in the spectral interval λ=3–5 µm

The influence of a gadolinium impurity on the electrical and luminescence characteristics of epitaxial structures made from narrow-gap n-InGaAsSb solid solutions grown by liquid-phase epitaxy on InAs substrates is investigated. The addition of gadolinium to the flux solution in the interval of concentrations 0<X _Gd ^l ⩽0.14 at. % has the effect of lowering the density of electrons in the InGaAsSb layers from (3–6)×10¹⁶ cm⁻³ to (7–8)×10¹⁵ cm⁻³ and increasing the carrier mobility from 32 000 cm²/(V·s) to 61 500 cm²/(V·s) (T=77 K). Also observed are a decrease in the half-width of the photoluminescence spectra from 25 meV to 12 meV and as much as a tenfold increase in their intensity (T=77 K). The electroluminescence intensity of LEDs fabricated from gadolinium-doped n-InGaAsSb/p-InAs epitaxial structures (T=300 K) increases approximately a factor of 2 relative to the undoped samples. Fiz. Tekh. Poluprovodn. 33, 1010–1013 (August 1999)     

Growth Optimization of an Electron Confining InN/GaN Quantum Well Heterostructure

The molecular beam epitaxy of In-face InN (0001) epilayers with optimized surface morphology, structural quality, and electrical properties was investigated. Namely, compact InN epilayers with atomically flat surfaces, grown in a step-flow mode, were obtained using stoichiometric fluxes of In and N and substrate temperatures in the range from 400°C to 435°C. Typical values for the electron concentration and the Hall mobility at 300 K were 4.3 × 10¹⁸ cm⁻³ and 1210 cm²/Vs, respectively. The growth mode of InN during the very first stage of the nucleation was investigated analytically, and it was found that the growth proceeds through nucleation and fast coalescence of two-dimensional (2-D)–like InN islands. The preceding conditions were used to grow an InN/GaN quantum well (QW) heterostructure, which exhibited well-defined interfaces. Schottky contacts were successfully fabricated using a 15-nm GaN barrier enhancement cap layer. Capacitance-voltage measurements revealed the confinement of electrons within the InN QW and demonstrated the capability to modulate the electron density within an InN channel. The sheet concentration of the confined electrons (1.5 × 10¹³ cm⁻²) is similar to the calculated sheet polarization charge concentration (1.3 × 10¹³ cm⁻²) at the InN/GaN interface. However, electrons may also originate from ionized donors with a density of 8 × 10¹⁸ cm⁻³ within the InN layer.     

Optical and Magnetic Properties of ZnO:V Prepared by Ion Implantation

We report on the optical and magnetic properties of the magnetic semiconductor Zn(V)O fabricated by implantation of 195 keV ₅₁V⁺ ions into bulk ZnO:Al grown by a hydrothermal technique. Two sets of the samples, containing N _d –N _a ∼ 10¹⁵ cm⁻³ and 10¹⁸ cm⁻³, were implanted to doses of 1 × 10¹⁵ cm⁻², 3 × 10¹⁵ cm⁻², and 1 × 10¹⁶ cm⁻². The ion implantation was performed at 573 K. To remove irradiation-induced defects, the samples were annealed in air at 1073 K. Photoluminescence (PL) measurements of Zn(V)O films were carried out at temperatures from 10 K to 300 K. The effects of implantation dose and free carrier concentration on the magnetic properties of Zn(V)O were studied using a superconducting quantum interference device magnetometer. Ferromagnetism has been observed in annealed highly conductive samples implanted to 1 × 10¹⁶ cm⁻². The PL studies of ZnO bulk samples implanted with V⁺ have revealed that thermal annealing at 1073 K restores to a large extent the optical quality of the material. A new emission line centered at 3.307 eV has been found in the PL spectrum of the highly conductive samples implanted to the dose of 1 × 10¹⁶ cm⁻², which is most probably due to complexes involving V ions.     

Properties of Bi-doped PbTe layers grown by liquid phase epitaxy under controlled Te vapor pressure

Effects of Bi doping in PbTe liquid-phase epitaxial layers grown by the temperature difference method under controlled vapor pressure (TDM-CVP) are investigated. For Bi concentrations in the solution, x_Bi, lower than 0.2 at.%, an excess deep-donor level (activation energy E_d≈0.03–0.04 eV) appears, and Hall mobility is low. In contrast, for x_Bi>0.2 at.%, Hall mobility becomes very high, while carrier concentration is in the range of 10¹⁷ cm⁻³. Inductive coupled plasma (ICP) emission analysis shows that, for x_Bi=1 at.%, Bi concentration in the epitaxial layer is as high as N_Bi=2.3–2.7 × 10¹⁹ cm⁻³. These results indicate that Bi behaves not only as a donor but also as an acceptor, and the nearest neighbor or very near donor-acceptor (D-A) pairs are formed, so that strong self-compensation of Bi takes place. Carrier concentration for highly Bi-doped layers shows a minimum at a Te vapor pressure of 2.2 × 10⁻⁵ torr for growth temperature 470°C, which is coincident with that of the undoped PbTe.     

Nuclear magnetic resonance spectra of 119Sn and 125Te in SnTe and SnTe:Mn

A study is reported of the nuclear magnetic resonance spectra of ¹¹⁹Sn and ¹²⁵Te in SnTe with hole concentrations p ₇₇=1.42×10²⁰−2.3×10²¹ cm⁻³ and in SnTe:Mn (N _Mn=0.5 and 5 at. %, p ₇₇=8×10²⁰ cm⁻³) at T=4.2–300 K. Considerable broadening of NMR lines due to hyperfine magnetic interactions between nuclear and electron spins was observed in SnTe with p ₇₇>2ײ⁰ cm⁻³. Asymmetric broadening of the resonance lines was observed in the rhombohedral phase of SnTe and SnTe:Mn. The temperature dependence of the NMR line width of ¹²⁵Te in SnTe:Mn is in agreement with the magnetic phase diagram for N _Mn=5 at. %. The superparamagnetic phase of SnTe:Mn is formed at T=20±2 K and the ferromagnetic phase is formed at T=4.2 K. Fiz. Tekh. Poluprovodn. 31, 1187–1191 (October 1997)     

Very low resistance ohmic contacts to n-GaN

Ohmic contacts with low resistance are fabricated on n-GaN films using Al/Ti bilayer metallization. GaN films used are 0.3 μm thick layers with carrier concentrations of 1 × 10¹⁹ cm⁻³ grown on the c-plane sapphire by ion-removed electron cyclotron resonance molecular beam epitaxy. The lowest value for the specific contact resistivity (ρ_c) of 1.2×10⁻⁸ Ω·cm² was obtained with furnace annealing at 500°C for 60 min. This result shows the effectiveness of high carrier concentration GaN layers and the low temperature annealing for the realization of low resistance ohmic contacts. Sputtering Auger electron spectroscopy analysis reveals that Al diffuses into Ti layer and comes into contact with the GaN surface.