Electrically active centers in Si:Er light-emitting layers grown by sublimation molecular-beam epitaxy

Electrically active centers in light-emitting Si:Er layers grown by sublimation molecular-beam epitaxy (SMBE) on single-crystal Si substrates have been investigated by admittance spectroscopy with temperature scanning and by DLTS. The total density of electrically active centers is defined by shallow donor centers with ionization energies of 0.016–0.045 eV. The effect of growth conditions and post-growth annealing on the composition and density of electrically active centers has been studied. Significant differences in composition of the electrically active centers with deep levels and in channels of energy transfer from the electron subsystem of a crystal to Er³⁺ ions between Si:Er layers grown by SMBE and ion implantation have been revealed.     

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.     

Electroluminescence at 1.54 μm in Si:Er/Si structures grown by sublimation molecular-beam epitaxy

In Si:Er/Si diode structures grown by sublimation molecular-beam epitaxy in a vacuum with a pressure of ～10^?7 mbar at temperatures 520–580°C, the intensity of room-temperature electroluminescence at 1.54 μm is studied as a function of the concentration and distribution of erbium and donor impurities in the space-charge region (SCR) and the SCR width. Methods for obtaining electroluminescence in diodes with a wide (0.1–1 μm) SCR are developed. The mean free path of electrons with respect to their interaction with Er centers and the threshold energy a free electron needs in order to excite an Er-shell electron are determined. The values of electric-field strength corresponding to breakdown in silicon p-i-n diodes with and without Er doping are obtained experimentally. A model describing the interaction of hot electrons with Er centers is suggested.     

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)     

Optical properties of silicon-doped (100) GaAs layers grown by molecular-beam epitaxy

The photoluminescence spectra of (100) GaAs layers, both undoped and doped with silicon, is investigated at T=77 K. It is found that along with the B-band, which corresponds to interband radiative recombination, the spectra of doped layers also exhibit a so-called Si-band located near hν⋍1.4 eV. In multilayer δ-doped structures, an additional band appears in the region hν⋍1.47–1.48 eV, which is called here the δ-band. The dependence of the energy positions, intensities, and shapes of these photoluminescence bands on the doping dose N _Si, laser excitation power, and temperature are investigated. It is shown that the Si-band is caused by optical transitions between the conduction band and a deep acceptor level (∼100 meV) connected with Si atoms on As sites. It is also established that the dependences of the shape and intensity of the δ-band on temperature and photoluminescence excitation power are identical to the corresponding dependences for the B-band. The behavior of the δ-band in the photoluminescence spectra is viewed as evidence of quantum-well effects in the δ-doped structures. Fiz. Tekh. Poluprovodn. 32, 1060–1063 (September 1998)     

Photoluminescence of GeSi/Si nanoclusters formed by sublimation molecular-beam epitaxy in GeH4 medium

The morphology and photoluminescence spectra of GeSi/Si(001) heterostructures with nanoclusters formed by sublimation molecular-beam epitaxy in GeH₄ medium are investigated as functions of growth conditions. It is established that the clusters nucleate by the Stranski-Krastanow mechanism; however, the coalescence processes substantially affect their morphology during further growth. Doubling of photoluminescence lines in nanoclusters associated with the radiative recombination inside the clusters and the blue shift of lines with increasing growth time associated with the Si diffusion from substrate into the clusters are observed. The conditions of forming uniform nanocluster arrays emitting at room temperature are determined.     

Electrical and optical properties of CdHgTe films grown by molecular-beam epitaxy on silicon substrates

The electrical and optical properties of epitaxial CdHgTe films grown on silicon substrates by molecular-beam epitaxy have been studied. The results of photoluminescence measurements are indicative of the high structural perfection of the films, and Hall data combined with low-energy ion treatment point to a low concentration of residual donors (??5 × 10¹⁴ cm^?3). Acceptor states supposedly related to the capture of impurities at structural defects typical of strongly lattice-mismatched heteroepitaxial structures are found in the films.     

Light-emitting Si:Er structures produced by molecular-beam epitaxy: High-resolution photoluminescence spectroscopy

Semiconductors - The photoluminescence spectra of light-emitting structures based on silicon layers doped with erbium in the course of growth by molecular-beam epitaxy at temperatures ranging from...     

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.     

Investigation of the structural properties of GaAs layers grown by molecular-beam epitaxy at low temperatures

The results of an investigation of the structural perfection of GaAs epitaxial films grown by molecular-beam epitaxy at low growth temperatures (240–300 °C) and various As/Ga flux ratios (from 3 to 13) are presented. Diffraction reflection curves display characteristic features for the samples before and after annealing in the temperature range from 300 to 800 °C. Hypotheses which account for these features are advanced. The range of variation of the arsenic/gallium flux ratio, in which low-temperature growth takes place under nearly stoichiometric conditions, is established. Fiz. Tekh. Poluprovodn. 31, 1168–1170 (October 1997)     

Optically active layers of silicon doped with erbium during sublimation molecular-beam epitaxy

A study is made of the electrical, optical, and structural properties of Si:Er layers produced by sublimation molecular-beam epitaxy. The Er and O contents in the layers, grown at 400–600°C, were as high as 5×10¹⁸ and 4×10¹⁹ cm⁻³, respectively. The electron concentration at 300 K was ∼10% of the total erbium concentration and the electron mobility was as high as 550 cm²/(V·s). Intense photoluminescence at 1.537 μm was observed from all the structures up to 100–140 K. The structure of the optically active centers associated with Er depended on the conditions under which the layers were grown. Fiz. Tekh. Poluprovodn. 33, 156–160 (February 1999)     

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.     

Special features of the sublimational molecular-beam epitaxy of Si and its potentialities for growing Si:Er/Si structures

The concentration of charge carriers and their Hall mobility in Si:Er/Si layers grown by sublimational molecular-beam epitaxy were investigated as functions of temperature in the range of 300–77 K. No electric activity of Er-containing luminescent centers was observed. The feasibility of precise control over impurity profiles in growing the p ⁺-n-n ⁺ electroluminescent structures is demonstrated.     

Electrical and optical properties of lodine doped CdZnTe layers grown by metalorganic vapor phase epitaxy

Electrical and photoluminescence properties of iodine doped CdZnTe (CZT) layers grown by metalorganic vapor phase epitaxy have been studied. Doped layers showed an n-type conductivity from the Zn composition x=0 (CdTe) to 0.07. Above x=0.07, resistivities of doped layers increased steeply up to 10⁶ Ω-cm. Resistivities of doped CZT layers were higher than those of undoped layers above x=0.6. Photoluminescence intensity of doped layers increased compared to undoped layers. Doped CdTe and ZnTe layers showed neutral donor bound exciton emission lines at the exciton related region. Also, these layers showed an increase in emission intensity at the donor acceptor pair recombination bands. Sharp emission lines were observed in doped CZT layers at around 1.49 eV. These emission lines were considered to be originated from GaAs substrates which were optically excited by the intense emission from doped CZT layers.     

ZnO growth on Si with low-temperature CdO and ZnO buffer layers by molecular-beam epitaxy

Low-temperature (LT) buffer-layer techniques were employed to improve the crystalline quality of ZnO films grown by molecular-beam epitaxy (MBE). Photoluminescence (PL) spectra show that CdO, as a hetero-buffer layer with a rock-salt structure, does not improve the quality of ZnO film grown on top. However, by using ZnO as a homo-buffer layer, the crystalline quality can be greatly enhanced, as indicated by PL, atomic force microscopy (AFM), x-ray diffraction (XRD), and Raman scattering. Moreover, the buffer layer grown at 450°C is found to be the best template to further improve the quality of top ZnO film. The mechanisms behind this result are the strong interactions between point defects and threading dislocations in the ZnO buffer layer.     

InGaAs/InGaAlAs/InAlAs/InP SCH-MQW laser diodes grown by molecular-beam epitaxy

InGaAs/InGaAlAs/InAlAs/InP separate-confinement hetero-structure-multiquantum-well (SCH-MQW) laser diodes have been fabricated by molecular-beam epitaxy (MBE), and room-temperature pulsed operation at 1.57 ?m has been achieved. This SCH-MQW laser is composed of InGaAs well layers, InGaAlAs quaternary barrier layers, and InAlAs and InP cladding layers.     

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.     

Structure and properties of silicon carbide grown on porous substrate by vacuum sublimation epitaxy

A SiC layer was grown by vacuum sublimation epitaxy on porous silicon carbide. A porous SiC layer about 10 μm thick was fabricated by electrochemical etching of an off-axis 6H-SiC substrate. The epitaxial layer was ∼ 10 μm thick. Structural and optical properties of the initial substrate and the porous and epitaxial layers were investigated by X-ray, IR-reflection and photoluminescence methods. An epitaxial SiC layer grown on porous SiC exhibits improved characteristics when compared to a SiC layer on a conventional substrate. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 7, 2002, pp. 812–816. Original Russian Text Copyright ? 2002 by Savkina, Ratnikov, Rogachev, Shuman, Tregubova, Volkova.     

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.