原料纯度对VPE ZnSe单晶薄膜发光和电学性能的影响

本文叙述了原料纯度对ZnSe外延膜的发光和电学性能的影响。随原料纯度提高,ZnSe外延膜的电阻率增大,同时PL光谱中与自由激子发射有关的Es带不断增强。这就表明,在我们实验条件下,ZnSe外延层的电导载流子主要来自于原料中施主杂质的污染而不是本征施主,当衬底温度较低时,原料中施主杂质的污染要比衬底中的Ga自扩散重要得多。随着原料纯度的提高,ZnSe外延膜电阻率增加,正是由于原料中施主杂质的减少。     

宽沟道SI-GaAs衬底上适于光发射机的BH激光器

目前,光发射机中的激光器有采用MOCVD和MBE方法生长的多量子阱激光器,用LPE法生长的BH激光器。我们根据现有的实验条件,为了制作单片集成的光发射机,在沟道SI-GaAs衬底上采用两次液相外延生长BH激光器,实现了表面平面化。在800℃一次外延生长四层。第一层n⁺-GaAs缓冲层,第二层N-GaAlAs下限制层,第三层非掺杂构GaAs有源层,第四层为P-GaAlAs上限制层。采用适当的腐蚀条件刻蚀出有源区最窄的燕尾形隐埋条。在二次外延中,我们仅装一槽GaAlAs源液,在晶片上仅停留一次便生长出两个掩埋层,且层间界面与有源区自对准。上层为N-GaAlAs,载流子浓度为10¹⁶cm^-3,下层为高阻伴随生长层。由于高阻伴随层的存在对电流产生了有有效的侧向限制作用,因此避免了通常的SiO₂膜沉积等一系列工艺,提高了成品率,减化了工艺程序。利用n型掩埋层和隐埋条区P型上限制层之间铝组分及载流子类型、浓度的差异,虽然做一种宽接触电极,但由于隐埋条区上有良好的欧姆接触,而在掩埋层上为非良欧姆接触,所以起到了一定的电流外限制作用。n型电极是从n⁺-GaAs层引出的。 这种沟道SI-GaAs衬底正装GaAlAs/GaAs BH激光器室温连续工作阈值电流为55mA,P-I曲线在100℃仍有良好的线性关系。     

Effect of AlGaAs barrier layer on the characteristics of InGaP/InGaAs/Ge triple junction solar cells

As an effort to improve the conversion efficiency of InGaP/InGaAs/Ge triple junction solar cells, we investigated the effect of AlGaAs barrier layer on the cell performance under concentrated light condition. Three different solar cells having upper tunnel junctions (TJs) as n⁺⁺-GaAs/p⁺⁺-AlGaAs layers, n⁺⁺-GaAs/p⁺⁺-GaAs layers and n⁺⁺-GaAs/p⁺⁺-GaAs/p⁺⁺-AlGaAs layers were prepared. Under concentrated light condition, open-circuit voltage (V_OC), fill factor (FF) and conversion efficiencies were higher for the sample with an AlGaAs barrier layer than the samples without an AlGaAs barrier layer. For the sample with an AlGaAs barrier layer, external quantum efficiency was higher than other two samples. Most of all, the sample with a TJ as n⁺⁺-GaAs/p⁺⁺-GaAs layers showed a very poor electrical performance, which was associated with an imperfect crystalline quality of the InGaP top cell layers.     

Series resistance calculation for the Metal-Insulator-Semiconductor Schottky barrier diodes

An accurate way of determining the series resistance R_s of Schottky Barrier Diodes (SBDs) with and without the interfacial oxide layer using forward current-voltage (I–V) characteristics is discussed both theoretically and experimentally by taking into account the applied voltage drop across the interfacial layerV _i. For the experimental discussion, the forward biasI–V characteristics of the SBDs with and without the oxide layer fabricated by LEC (the Liquid-Encapsulated Czochralski) GaAs were performed. The SBD without the oxide layer was fabricated to confirm a novel calculation method. For the theoretical discussion, an expression ofV _i was obtained by considering effects of the layer thickness and the interface state density parameters on forward biasI–V of the SBDs. The valueR _s of the SBD with interfacial oxide layer was seen to be larger than that of the SBD without the interfacial oxide layer due to contribution of this layer to the series resistance. According to the obtained theoretical formula, the value ofV _i for the SBD with the oxide layer was calculated and it was subtracted from the applied voltage values V and then the value ofR _s was recalculated. Thus, it has been shown that this new value ofR _s is in much closer agreement with that determined for the SBD without the oxide layer as predicted. Furthermore, the curves of the interface states energy distribution of each sample are determined. It was concluded that the shape of the density distribution curve and order of magnitude of the density of the interface states in the considered energy range are in close agreement with those obtained by others for Au/n-GaAs Schottky diodes by Schottky capacitance spectroscopy.     

ZnO-based heterojunction light-emitting diodes on p-SiC(4H) grown by atomic layer deposition

Atomic layer deposition was used to grow n-type Al-doped ZnO (n-ZnO) and undoped ZnO (i-ZnO) layers on p-type 4H-SiC substrates, to fabricate n-ZnO/p-SiC and n-ZnO/i-ZnO/p-SiC heterojunction light-emitting diodes (LEDs). Electroluminescence (EL) from the n-ZnO/p-SiC LED originated from radiative recombination of donor–acceptor pairs in SiC due to the predominant electron injection from n-ZnO into p-SiC. On the other hand, the n-ZnO/i-ZnO/p-SiC LED exhibited dominant ultraviolet (UV) emission at 393 nm from ZnO. This difference is attributable to the insertion of the undoped i-ZnO layer between n-ZnO and p-SiC, leading to the injection of holes from p-SiC and electrons from n-ZnO into the i-ZnO layer and thus the generation of UV EL from ZnO.     

Oxidation of silicon surface with atomic oxygen radical anions

The surface oxidation of silicon （Si） wafers by atomic oxygen radical anions （O- anions） and the preparation of metal-oxide-semiconductor （MOS） capacitors on the O-oxidized Si substrates have been examined for the first time. The O- anions are generated from a recently developed O- storage-emission material of [Ca24Al2sO64]^4＋·4O^- （Cl2A7-O^- for short）. After it has been irradiated by an O- anion bean： （0.5 μA/cm^2） at 300℃ for 1-10 hours, the Si wafer achieves an oxide layer with a thickness ranging from 8 to 32 nm. X-ray photoelectron spectroscopy （XPS） results reveal that the oxide layer is of a mixture of SiO2, Si2 O3, and Si2O distributed in different oxidation depths. The features of the MOS capacitor of 〈Al electrode/SiOx/Si〉 are investigated by measuring capacitance-voltage （C - V） and current-voltage （I - V） curves. The oxide charge density is about 6.0 × 10^1 cm^-2 derived from the （C - V curves. The leakage current density is in the order of 10^-6 A/cm^2 below 4 MV/cm, obtained from the I - V curves. The O- anions formed by present method would have potential applications to the oxidation and the surface-modification of materials together with the preparation of semiconductor devices.     

Visualization of a Berezinskii–Kosterlitz–Thouless Topological Phase Transition in a Josephson Medium: Detection of an Anomalous Temperature Dependence of the Magnetoresistance of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7–δ</Subscript> Granular High-Temperature Superconductors

The density of states of the valence band of a p-GaAs layer formed on an n-GaAs surface owing to the bombardment by 2500-eV Ar⁺ ions has been studied by photoelectron spectroscopy. A number of peaks have been detected in the spectrum of the edge of the valence band in the binding energy range E_V < 1.2eV. Their number and energy positions correspond to the quantum confinement levels calculated for a hole quantum well on the surface with the width about the ion penetration depth R_p = 3.6nm. Electronic transitions from these levels to the bottom of the conduction band have been revealed in the spectrum of characteristic energy losses of electrons reflected from the surface. Thus, it has been shown that the action of the argon ion beam on n-GaAs results in the formation of a quantum well on the surface.     

Determination of deep electron traps in GaAs by time-resolved capacitance measurement

A useful technique of determining the energy levels and the spatial density distributions of multiple electron traps in semi-conductor has been developed using the time-resolved measurement of the Schottky barrier junction capacitance, and this technique has been applied to characterize the electron traps inn-GaAs. In the present technique, the energy levels are determined from single scan of temperature, and the density distributions are calculated from a set of capacitance-voltage relationships. Four traps which lay at 0.39, 0.73, 0.79, and 0.58 eV below the conduction band edge were observed in boat grown or vapor phase epitaxially grown crystals. Many layers which were obtained by a vapor phase epitaxial growth system with N₂ carrier gas were measured and it was found that almost all of them include the 0.73 eV and the 0.79 eV trap with the density between 1×10¹³ and 2×10¹⁵ cm⁻³.     

Injection electroluminescence from quantum-size InGaAs/GaAs structures with metal/semiconductor and metal-oxide-semiconductor junctions

Electroluminescence from forward-biased diode structures with Au(Ni)/GaAs and Au(Ni)/tunneling-thin oxide/GaAs junctions has been studied. The possibility of luminescence amplification from the Schottky diodes by introducing a tunneling-thin anode-oxide or heavily doped p ⁺-GaAs layer between the metal and semiconductor have been demonstrated. The studies of the temperature dependence of electroluminescence and the I-W curves indicate that the amplification of the electroluminescence intensity from the above structures may be associated with lowering the potential barrier for the minority carriers under the forward bias of the Schottky barrier.     

Interface of anodic sulfide-oxide on n-type InSb

A novel anodic sulfidization process for forming native sulfide-oxide films on n-type InSb is described. The results of Auger electron spectroscopy analysis indicate that native sulfide-oxide films are formed from aqueous sulfide solutions. The measured capacitance-voltage characteristics of metal-insulator-semiconductor devices indicate that the films have a low fixed surface charge density of the order of 3×10¹⁰ cm^–2 and small hysteresis. The native sulfide-oxide films leave the surface of n-type InSb practically at flatband and in this respect are superior to the passivation layers of anodic oxide and direct plasma SiN _x . The interface between InSb and its native sulfide-oxide in combination with plasma CVD SiN _x has excellent electrical properties.     

Study of S ion-assisted sulfurization of n-GaAs (1 0 0) surface

The chemical structure and site location of sulfur atoms on n-GaAs (1 0 0) surface treated by bombardment of S⁺ ions over their energy range from 10 to 100 eV have been studied by X-ray photoelectron spectroscopy and low energy electron diffraction. The formation of Ga-S and As-S species on the S⁺ ion bombarded n-GaAs surface is observed. An apparent donor doping effect is observed for the n-GaAs by the 100 eV S⁺ ion bombardment. It is found that the S⁺ ions with higher energy are more effective in the formation of Ga-S species, which assists the n-GaAs (1 0 0) surface in reconstruction into an ordered (1 × 1) structure upon subsequent annealing. The treatment is further extended to repair Ar⁺ ion damaged n-GaAs (1 0 0) surface. It is found that after a n-GaAs (1 0 0) sample is damaged by 150 eV Ar⁺ ion bombardment, and followed by 50 eV S⁺ ion treatment and subsequent annealing process, finally an (1 × 1) ordering GaAs (1 0 0) surface with low surface states is obtained.     

Frequency dependence of the surface states at the N-type Si-SiO2 interface

The response of the surface states at then-type Si-SiO₂ interface to the different a.c. signal frequencies has been studied. The response values have been computed from both the measured capacitance voltage (C-V) and conductance-voltage (G-V) techniques. The results presented show that the frequency response of the effective density of states to different a.c. signal frequencies is proportional to the log of the applied frequencies.     

Structure and optoelectronic properties of Si/O superlattice

We have carried out structural study of the Si/O semiconductor atomic superlattices (SAS) with up to 18 Si/O layers fabricated by molecular beam epitaxy and in situ oxygen exposure on both Sb-doped and undoped Si buffer layers, and correlated the results with our photoluminescence, electroluminescence (EL) and I–V data. The Si/O SAS is a new type of superlattice, where monolayers of oxygen are sandwiched between the Si layers. High-resolution cross-sectional transmission electron microscopy (TEM) study has confirmed the presence of the superlattice and shown epitaxy in the Si/O superlattices. The high structural quality of the layers grown on the undoped Si buffer layers with low density of stacking faults—less than 10⁷/cm²—was established by TEM. Although structure perfection is very important allowing this new class of superlattices to be extended to other systems, it is important to point out that a 9-period SAS-based EL device with emission of light in green has been life-tested with stable output for over 1 year of continuous operation. The Si/O superlattice also serves as an epitaxially grown insulating layer as possible replacement of silicon-on-insulator. Together with the tailor-made effective band gap, this epitaxially grown superlattice may serve as future silicon-based three-dimensional integrated circuits.     

GaAs/GaAlAs双异质结发光管退化特性的研究

本文研究了GaAs/GaAlAs双异质结发光管的退化特性。有快、慢二种退化类型。器件的慢退化是由于有源区有暗缺陷(DSD)产生和长大,引起光功率下降。文中研究了老化过程中I-V特性和I-P特性与EL图象的变化规律,并与相同结构的InP/InGaAsP双异质结发光管的退化特性进行了比较,结果表明:它们有着不同的退化机理。     

Impact of rough silicon buffer layer on electronic quality of GaAs grown on Si substrate

The electronic and the structural properties of n-GaAs layers grown on rough surface of silicon substrate by molecular beam epitaxy (MBE) has been investigated by photoluminescence (PL), time resolved photoluminescence (TRPL) and high resolution X-ray diffraction (HRXRD). The relationship between electronic and structural properties of the n-GaAs layer was checked, showing that the defect density is a strong cause for trapping the minority carriers. The impact of introducing intermediate rough silicon layer between silicon substrate and n-GaAs layer on the electronic properties was observed, showing that the structure grown on rough Si involves higher lifetime than those developed on flat silicon substrate. Such structure could be used for economic solar cells fabrication.     

Study of density of interface states in MOS structure with ultrathin NAOS oxide

The quality of the interface region in a semiconductor device and the density of interface states (DOS) play important roles and become critical for the quality of the whole device containing ultrathin oxide films. In the present study the metal-oxide-semiconductor (MOS) structures with ultrathin SiO₂ layer were prepared on Si(100) substrates by using a low temperature nitric acid oxidation of silicon (NAOS) method. Carrier confinement in the structure produces the space quantization effect important for localization of carriers in the structure and determination of the capacitance. We determined the DOS by using the theoretical capacitance of the MOS structure computed by the quantum mechanical approach. The development of the density of SiO₂/Si interface states was analyzed by theoretical modeling of the C-V curves, based on the superposition of theoretical capacitance without interface states and additional capacitance corresponding to the charges trapped by the interface states. The development of the DOS distribution with the passivation procedures can be determined by this method.     

Frequency-tunable terahertz electromagnetic wave emitters based on undoped GaAs/n-type GaAs epitaxial layer structures utilizing sub-picosecond-range carrier-transport processes

We have investigated sub-picosecond-range carrier-transport processes in undoped GaAs/n-type GaAs (i-GaAs/n-GaAs) epitaxial layer structures with various i-GaAs-layer thicknesses d ranging from 200 to 2000 nm, focusing on the relation between carrier-transport processes and terahertz electromagnetic wave frequency. Initially, using numerical simulation and photoreflectance measurement, we confirm that a decrease in d enhances the built-in electric field in the i-GaAs layer. In the time-domain terahertz waveform, it is observed that the intense monocycle oscillation induced by the surge current of photogenerated carriers, the so-called first burst, is followed by the oscillation patterns originating from the coherent GaAs longitudinal optical (LO) phonon. From the Fourier power spectra of the terahertz waveforms, it is clarified that the decrease in d causes a high frequency shift of the band of the first burst. Consequently, we conclude that, in the sub-picosecond time range, the photogenerated carriers are monotonously accelerated by the built-in electric field without being affected by intervalley scattering. The present conclusion signifies that the frequency-tunable terahertz emitters are realized by controlling i-GaAs-layer thickness. We also find the intensity of the coherent LO phonon band is enhanced by a decrease in d.     

Deep levels in gallium arsenide by capacitance methods

The three capacitance methods, i.e., TSCAP, PHCAP, and transient capacitance measurements, are applied to determine electronic properties of deep levels inn-GaAs. In the boat-grown wafer detected are the 0.30 eV electron trap withN _T =3.6×10¹⁶ cm^?3 andS _n =2.4×10^?15 cm², and the 0.75 eV electron trap withN _T =2.0×10¹⁶ cm^?3 andS _n =1.2×10^?14 cm². In the epitaxial wafer, the 0.45 eV hole trap is detected withN _T >1.5×10¹³ cm^?3 andS _p =1.4×10^?14 cm² as well as the 0.75 eV electron trap withN _T =2.4×10¹³ cm^?3.     

Chemical effects during formation of the electronic surface structure of III–V semiconductors in a sulfide solution

The electronic properties of the (100) surface of n-GaAs, p-GaAs, and n-InP semiconductors treated with various sulfide solutions have been studied. Sulfide treatment was shown to increase the photoluminescence intensity, decrease the depth of the near-surface depleted region in the semiconductor, and shift the surface Fermi level toward the conduction band. These effects are the stronger, the higher the sulfur chemical activity in the solution. Fiz. Tverd. Tela (St. Petersburg) 41, 875–878 (May 1999)