Exciton spectra and electrical conductivity of epitaxial silicon-doped GaN layers

Optical spectra and electrical conductivity of silicon-doped epitaxial gallium nitride layers with uncompensated donor concentrations N _D — N _A up to 4.8 × 10¹⁹ cm^?3 at T ≈ 5 K have been studied. As follows from the current-voltage characteristics, at a doping level of ～3 × 10¹⁸ cm^?3 an impurity band is formed and an increase of donor concentration by one more order of magnitude leads to the merging of the impurity band with the conduction band. The transformation of exciton reflection spectra suggests that the formation of the impurity band triggers effective exciton screening at low temperatures. In a sample with N _D — N _A = 3.4 × 10¹⁸ cm^?3, luminescence spectra are still produced by radiation of free and bound excitons. In a sample with N _D — N _A = 4.8 × 10¹⁹ cm^?3, Coulomb interaction is already completely suppressed, with the luminescence spectrum consisting of bands deriving from impurity-band-valence band and conduction-band-valence band radiative transitions.     

Ionization mechanisms of aluminum acceptor impurity in silicon

Processes of ionization of shallow acceptor centers (ACs) in silicon are studied. In crystalline silicon samples with phosphorus (1.6×10¹³, 2.7×10¹³, and 2.3×10¹⁵cm^?3) and boron (1.3×10¹⁵cm^?3) impurities, _μAl impurity atoms were produced by implantation of negative muons. It is found that thermal ionization is the main mechanism for ionizing the Al acceptor impurity in both p-type and n-type silicon with an impurity concentration of ?10¹⁵cm^?3 at T>45 K. The thermal ionization rate of Al ACs in Si varies from ～10⁵ to ～10⁶s^?1 in the temperature range 45–55 K.     

Magnetic moment relaxation of a shallow acceptor center in heavily doped silicon

Results of studying the temperature dependence of the residual polarization of negative muons in crystalline silicon with germanium (9×10 ¹⁹ cm ^?3 ) and boron (4.1×10 ¹⁸ , 1.34×10 ¹⁹ , and 4.9×10 ¹⁹ cm ^?3 ) impurities are presented. It is found that, similarly to n-and p-type silicon samples with impurity concentrations up to ～10 ¹⁷ cm ^?3 , the relaxation rate ν of the magnetic moment of a _μ Al acceptor in silicon with a high impurity concentration of germanium (9×10 ¹⁹ cm ^?3 ) depends on temperature as ν～T ^q , q≈3 at T=(5–30) K. An increase in the absolute value of the relaxation rate and a weakening of its temperature dependence are observed in samples of degenerate silicon in the given temperature range. Based on the experimental data obtained, the conclusion is made that the spin-exchange scattering of free charge carriers makes a significant contribution to the magnetic moment relaxation of a shallow acceptor center in degenerate silicon at T?30 K. Estimates are obtained for the effective cross section of the spin-exchange scattering of holes (σ _h ) and electrons (σ _e ) from an Al acceptor center in Si: σ _h ～10^?13 cm² and σ _e ～8×10^?15 cm² at the acceptor (donor) impurity concentration n _a (n _d )～4×10¹⁸ cm^?3.     

Electrical properties of n-type vapor-grown gallium nitride

Hall measurements are reported for undoped and Zn-doped vapor-grown single crystal GaN on (0001) Al₂O₃ layers with 298 K carrier concentrations (n-type) between 1·4×10¹⁷cm^?3 and 9×10¹⁹ cm^?3. Then n～10¹⁷ cm^?3 crystals (undoped) have mobilities up to μ～440 cm²/V sec at 298 K. Their conduction behavior can be described by a two-donor model between 150 and 1225 K and by impurity band transport below 150 K. Crystals with n≥8×10¹⁸ cm^?3 show metallic conduction with no appreciable variation in n or μ between 10 and 298 K.Results of mass spectrographic analyses indicate that the total level of impurities detected is too low to account for the observed electron concentration at the n～10¹⁹ cm^?3 level, and suggest the presence of a high concentration of native donors in these crystals. No significant reduction in carrier concentration was achieved with Zn doping up to concentrations of ～10²⁰ cm^?3 under the growth conditions of the present work, and no evidence was found to indicate that high conductivity p-type behavior may be achieved in GaN. The influence of factors such as growth rate, crystalline perfection and vapor phase composition during growth on the properties of the layers is described.     

Effect of the doping level on temperature bistability in a silicon wafer

The influence of the doping level on the effect of the temperature bistability in a silicon wafer upon radiative heat transfer between the wafer and the elements of the heating system is studied. Theoretical transfer characteristics are constructed for a silicon wafer doped with donor and acceptor impurities. These characteristics are compared with the transfer characteristics obtained during heating and cooling of wafers with the hole conduction (with dopant concentrations of 10¹⁵, 2 × 10¹⁶, and 3 × 10¹⁷ cm^?3) and electron conduction (with impurity concentrations of 10¹⁵ and 8 × 10¹⁸ cm^?3) in a thermal reactor of the rapid thermal annealing setup. It is found that the width and height of the hysteresis loop decrease with increasing dopant concentration and are almost independent of the type of conduction of the silicon wafer. The critical value of the impurity concentration of both types is 1.4 × 10¹⁷ cm^?3. For this concentration, the loop width vanishes, and the height corresponds to the minimal value of the temperature jump (～200 K). The mechanism of temperature bistability in the silicon wafer upon radiative heat transfer is discussed.     

Effects of silicon negative ion implantation in semi-insulating gallium arsenide

ABSTRACT

In the present work, effects of silicon negative ion implantation into semi-insulating gallium arsenide (GaAs) samples with fluences varying between 1?×?10¹⁵ and 4?×?10¹⁷?ions?cm^?2 at 100?keV have been described. Atomic force microscopic images obtained from samples implanted with fluence up to 1?×?10¹⁷?ion?cm^?2 showed the formation of GaAs clusters on the surface of the sample. The shape, size and density of these clusters were found to depend on ion fluence. Whereas sample implanted at higher fluence of 4?×?10¹⁷?ions?cm^?2 showed bump of arbitrary shapes due to cumulative effect of multiple silicon ion impact with GaAs on the same place. GXRD study revealed formation of silicon crystallites in the gallium arsenide sample after implantation. The silicon crystallite size estimated from the full width at half maxima of silicon (111) XRD peak using Debye-Scherrer formula was found to vary between 1.72 and 1.87?nm with respect to ion fluence. Hall measurement revealed the formation of n-type layer in gallium arsenide samples. The current–voltage measurement of the sample implanted with different fluences exhibited the diode like behavior.     

Beam transport

Abstract

Dopant distribution, electrical activity and damage annealing of high-dose (～5 × 10¹⁵ cm²) Ga-implanted silicon samples annealed by conventional thermal annealing have been studied by alpha particle back-scattering, differential Hall effect and ellipsometry measurements. Back-scattering spectra show that there is no long tail of Ga atoms in the as-implanted samples. Upon annealing these samples the damaged amorphous layer recrystallizes at about 570°C by solid phase epitaxy. During the epitaxial regrowth the dopant atom distribution seems to be modified. Further, very high levels of electrical activaton of Ga-atoms (～3 × 10²⁰ cm^?3), much higher than the maximum solubility limit of Ga in Si (4.5 × 10¹⁹ cm^?3), is achieved by thermal annealing of the sample at ～570°C. This is comparable to the doping achieved by laser annealing of the Ga implanted Si. All the above three measurements show that there is residual damage in the high dose (?10¹⁵cm^?2) implanted samples after the recrystallization at about 570°C. This may be related to strain in the lattice at the high concentrations of metastable substitutional Ga atoms. Annealing at higher temperature reduces the electrical activity of Ga atoms, possibly by driving out the metastably high substitutional concentrations of Ga-atoms into electrically inactive clusters or precipitates.     

Study of hydrogenated AlN as an anti‐reflective coating and for the effective surface passivation of silicon

Stacks of aluminum oxide and silicon nitride are frequently used in silicon photovoltaics. In this Letter, we demonstrate that hydrogenated aluminum nitride can be an alternative to this dual‐layer stack. Deposited on 1 Ω cm p‐type FZ silicon, very low effective surface recombination velocities of 8 cm/s could be reached after firing at 820 °C. This excellent passivation is traced back to a high density of fixed charges at the interface of approximately –1 × 10¹² cm^–2 and a very low interface defect density below 5 × 10¹⁰ eV^–1 cm^–2. Furthermore, spectral ellipsometry measurements reveal that these aluminum nitride layers have ideal optical properties for use as anti‐reflective coatings. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal lattice defects and Hall mobility of electrons in Si: Er/Si layers grown by sublimation molecular-beam epitaxy

The density of crystal lattice defects in Si: Er layers grown through sublimation molecular-beam epitaxy at temperatures ranging from 520 to 580°C is investigated by a metallographic method, and the Hall mobility of electrons in these layers is determined. It is found that the introduction of erbium at a concentration of up to ～5 × 10¹⁸ cm^?3 into silicon layers is not accompanied by an increase in the density of crystal lattice defects but leads to a considerable decrease in the electron mobility.     

Silicon negative ion implantation induced vacancy defects in thermally grown SiO2 thin films

ABSTRACT

Thermally grown SiO₂ thin films on a silicon substrate implanted with 100?keV silicon negative ions with fluences varying from 1?×?10¹⁵ to 2?×?10¹⁷ ions cm^?2 have been investigated using Electron spin resonance, Fourier transforms infrared and Photoluminescence techniques. ESR studies revealed the presence of non-bridging oxygen hole centers, E′-centers and P_b-centers at g-values 2.0087, 2.0052 and 2.0010, respectively. These vacancy defects were found to increase with respect to ion fluence. FTIR spectra showed rocking vibration mode, stretching mode, bending vibration mode, and asymmetrical stretching absorption bands at 460, 614, 800 and 1080?cm^?1, respectively. The concentrations of Si–O and Si–Si bonds estimated from the absorption spectra were found to vary between 11.95?×?10²¹ cm^?3 and 5.20?×?10²¹ cm^?3 and between 5.90?×?10²¹ cm^?3 and 3.90?×?10²¹ cm^?3, respectively with an increase in the ion fluence. PL studies revealed the presence of vacancies related to non-bridging oxygen hole centers, which caused the light emission at a wavelength of 720?nm.     

离子注入n型GaN光致发光谱中宽黄光发射带研究

利用离子注入方法和光致发光技术系统研究了注入离子对n型GaN宽黄光发射带的影响.实验采用的注入离子为：N，O，Mg，Si和Ga，剂量分别为10¹³，10¹⁴，10¹⁵和10¹⁶/cm²，注入温度为室温.注入后的样品在900 ℃流动氮气环境下进行热退火，退火时间为10 min，并对退火前后的样品分别进行室温光致发光测量.通过实验数据的分析，独立提出了提取注入离子对晶体黄光发光特性影响的半经验模型.利用该模型导出的公式，可以确定注入的N，O，Ga，Mg和Si离子对黄光发射带的影响随注入剂量的变化关系以及该影响的相对强弱. 关键词： 氮化镓 光致发光谱 离子注入     

Evolution of infrared spectra and optical emission spectra in hydrogenated silicon thin films prepared by VHF-PECVD

A series of hydrogenated silicon thin films with varying silane concentrations have been deposited by using very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The deposition process and the silicon thin films are studied by using optical emission spectroscopy (OES) and Fourier transfer infrared (FTIR) spectroscopy, respectively. The results show that when the silane concentration changes from 10% to 1%, the peak frequency of the Si—H stretching mode shifts from 2000 cm ^{- 1} to 2100 cm ^{- 1}, while the peak frequency of the Si—H wagging—rocking mode shifts from 650 cm ^{- 1} to 620 cm ^{- 1}. At the same time the SiH^*/H_α intensity ratio in the plasma decreases gradually. The evolution of the infrared spectra and the optical emission spectra demonstrates a morphological phase transition from amorphous silicon (a-Si:H) to microcrystalline silicon (μc-Si:H). The structural evolution and the μc-Si:H formation have been analyzed based on the variation of H_α and SiH^* intensities in the plasma. The role of oxygen impurity during the plasma process and in the silicon films is also discussed in this study.     

Structural and electrical characteristics of a hyperdoped silicon surface layer with deep donor sulfur states

Inhomogeneous hyperdoping of a 100-nm-thick silicon surface layer with sulfur atoms at concentrations above 2 × 10²¹ cm^?3 was obtained via its femtosecond laser ablation in a sulfur-containing organic solvent. Infrared transmission spectroscopy reveals distinct interband absorption peaks of donor sulfur states, which are absent in the initial crystalline silicon, and a broad absorption band of free carriers with a concentration of ～10¹⁸ cm^?3. The rather low free-carrier concentration is related to equilibrium room-temperature ionization of localized donor sulfur states, preserving their nondegenerate character owing to the strong electronion binding in the donor states.     

Formation and nature of swirl defects in silicon

Point defect agglomerates in dislocation-free silicon crystals, usually called “swirls”, have been investigated by means of high-voltage electron microscopy. It was found that a single swirl defect consists of a dislocation loop or a cluster of dislocation loops. By contrast experiments it could be shown that these loops are formed by agglomeration of self-interstitial atoms. Generally the loops have a/2〈110〉 Burgers vectors, but in specimens with high concentrations of carbon (～10¹⁷ cm^?3) and oxygen (～10¹⁶ cm^?3) also dislocation loops including a stacking fault were observed. In crystals grown at growth rates higher thanv=4 mm/min no swirls are observed; lower growth rates do not markedly affect the size and shape of the dislocation loops. With decreasing impurity content (particulary of oxygen and carbon) the swirl density decreases, whereas the dislocation loop clusters become larger and more complex. A model is presented which describes the formation of swirls in terms of agglomeration of silicon self-interstitials and impurity atoms.     

A study of the nitridation of silicon surfaces by low-energy electron diffraction and auger electron spectroscopy

Low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) have been used to study the initial stages of the nitridation of silicon. Most of the experiments involved pressures of 10^?5?10^?7 torr of ammonia and silicon temperatures in the range 800–1100°C. An earlier study of the nitridation of the Si (111) surface, has been extended to allow comparison between the (111), (311) and (100) faces of silicon. These surfaces provide a series of unit meshes with different shapes and symmetries while retaining some common geometrical features. Of particular interest for epitaxial theory is the growth of an impurity induced nitride structure, which is common to both Si(111) and Si (311). This may be explained if the nucleation and orientation of the niti ide are determined by the geometry of localised sites, common to both substrates. Subsequent growth of the nitride layer is then dominated by intra-layer bonding, so that the difference in substrate symmetries has little effect.     

Strain-induced anodization of SiGe/Si multiple layers to form high density SiGe/Si heterogeneous nanorods

SiGe/Si heterogeneous nanostructures are prepared by electrochemical anodization of SiGe/Si multiple layers grown by ultra-high vacuum chemical vapor deposition. Nanorods with densities up to ～2×10¹¹ cm^?2 have been observed with a relatively uniform distribution confirmed by scanning electron microscope images of both top and cross-sectional views. The samples show visible photoluminescence with multiple peaks and narrow widths which is related to the interference effect. Finally, a model is proposed to explain the role of strain during the anodization of SiGe/Si multiple layers.     

Resonant and localised modes due to boron in gallium arsenide

Silicon-doped n-type GaAs crystals pulled from a melt encapsulated with boric oxide exhibit an IR absorption band at 123 cm^?1 as well as a number of localised-mode bands associated with boron and silicon. Evidence is presented which leads us to attribute the band at 123 cm^?1 to a resonant mode associated with isolated B atoms on Ga sites. Other crystals containing high concentrations of silicon or phosphorous did not show such an absorption band. The results are discussed briefly in terms of the simple mass defect model for impurity vibrations.     

Beta-induced reduction in Cu/Si-structure adhesion

The effect of low-flux (I ～ 1.8 × 10⁵ cm^?2 s^?1) β irradiation on the process of the delamination of thin copper films (with a thickness of ～100 nm) from a silicon substrate under indentation by a Berkovich pyramid is studied. It is revealed that irradiation with a fluence of F = 3.24 × 10¹⁰ cm^?2 leads to an increase in the perimeter and area of the copper-film delaminations formed upon penetration of the indenter. This indicates a β-induced reduction in adhesion in the Cu/Si structure.     

Impurity redistribution in Pb implanted and annealed silicon

Reordering of 〈111〉 silicon, implanted with Pb ions at energies >100 keV and fluences ～5 × 10¹⁵ cm^?2 is accompanied by substantial impurity indiffusion in addition to pronounced outdiffusion and accumulation at the near surface region.     

Investigation of gallium arsenide single crystals with various crystallographic orientations, after implantation of silicon ions and pulsed photon annealing

The results of experimental investigations of gallium arsenide single crystals with the orientations (100), (311)A, (211)A, (111)A, and (221)A are presented. The crystals were doped with silicon ions on the Iolla-3M setup (ion energy 75 keV, ion beam density 1 μA/cm², implantation dose 1.2×10³ cm⁻²) at room temperature and annealed on the Impul’s-5 setup at 950°C. Raman scattering and low-temperature photoluminescence methods established that the highest electrical activity of the implanted silicon under identical implantation and annealing conditions obtains for (100) and (311)A gallium arsenide. In the process n-type layers are produced. Zh. Tekh. Fiz. 69, 78–82 (May 1999) Deceased.