Polarization photosensitivity of a-Si:H/c-Si heterojunctions

The photosensitivity of heterojunctions formed by depositing thin amorphous films on silicon crystalline substrates is investigated. It is found that heterojunctions exhibit polarization photosensitivity, which is observed at an oblique incidence of the linearly polarized radiation on their receiving plane. The induced photopleochroism of heterojunctions increases quadratically with an increase in the angle of incidence θ and reaches 60% for θ=80°. It is concluded that the heterojunctions obtained can be used as the broadband photodetectors of the linearly polarized radiation.     

Adaptation of admittance analysis to extract interface traps of a-Si:H/c-Si heterojunctions

Complete admittance expressions, adapted from the equations previously presented for Metal/Oxide/Semiconductor (MOS) structure, were derived and modified admittance approach was successfully applied on a-Si:H/c-Si heterojunction to deduce surface state density (N_ss) by employing capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements. Through the approach, N_ss was determined as 6×10¹² cm⁻² eV⁻¹ that was mutually checked by continuum model, used previously for evaluating N_ss in MOS structure. Furthermore, locating such an amount at the interface of a-Si:H and c-Si, experimentally measured C–V curve was reproduced through AFORS-HET simulation program. Presence of such a large amount of N_ss was originated due to native oxide layer, confirmed through spectroscopic elipsometry measurement.     

Photosensitivity of a-Si:H/n-InSe heterocontacts

Rectifying photosensitive structures were obtained for the first time by bringing the surfaces of thin films of amorphous hydrogenated silicon deposited onto the silica-glass substrates into direct optical contact with the InSe natural-cleavage surface. Spectral dependences of the quantum efficiency of the obtained heterocontacts were studied, and the prospects for the use of the new a-Si:H/n-InSe heterocontacts in solar cells were assessed.     

氢化非晶碳膜与硅的界面特性

利用直流辉光放电分解碳氢气体来淀积ａ－Ｃ：Ｈ膜，通过测量Ａｌ／ａ－Ｃ：Ｈ／ＳｉＭＩＳ结构的高频Ｃ－Ｖ曲线讨论了ａ－Ｃ：Ｈ／Ｓｉ界面的电子特性，结果表明ａ－Ｃ：Ｈ／Ｓｉ膜有可能用作半导体器件的表面钝化膜。     

a—Si：H／c—Si异质结的高频C—V特性

测量了GD a-Si:H/n-c-Si异质结的高频C-V特性,由平带电压的偏移,计算了有效表面电荷和表面态密度,应用突变异质结能带模型对结果作了分析.     

Negative capacitance peculiarities in a-Si:H/c-Si rectifier structure

Nontrivial negative capacitance (NC) effect, observed in a-Si:H/c-Si heterostructure devices, is discussed emphasizing the theoretical interpretation of experimental data. To explain NC effect, we have performed dark current voltage (I-V) and admittance measurements (C-V, G-V, C-f and G-f). The calculated values of series resistance (R_s) and barrier height (Φ_Bo) have the values from 100 to 114.7 Ω and 0.94 to 0.83 eV, respectively. Also, below 50% helium dilution rate, diode ideality factor (n) becomes bigger than 2, because tunneling at junction interface plays a major role. The measured room temperature (294 K) dark I-V result has been used during the fitting process for suggested capacitance model (Eq. (18)). The measured NC values exhibit strongly voltage depended behavior. This unexpected behavior is attributed to the presence of inductively coupled space charge region which might possibly be stemmed from the helium diluted a-Si:H material. It is seen that the measured NC values are well fitted with suggested capacitance model (Eq. (18)). Application of suggested correction formula on to experimental C-V data yields satisfactory results. It is shown that the calculated inductance values of the investigated device range from 10 to 42 μH and after correction, NC values are no longer observed in the C_d-V data.     

红外反射镜a-C·H/Au/Cu/Cu的设计与实验室工艺

本文报导将非晶碳氢膜(a-C:H)用作红外反射镜Au/Cu的表面保护膜的设计计算、实验室制备工艺研究、及有关性能测试结果。我们的第一阶段工作结果表明,a-C:H/Au/Cu在实用上是有价值的,值得继续进行工作。     

Scanning tunneling spectroscopy of a-C:H and a-C:(H, Cu) films prepared by magnetron sputtering

Scanning tunneling spectroscopy was used to study a-C:H and a-C:(H, Cu) films under atmospheric conditions; these films were formed on semiconductor (Si) and metallic (Cr/Si) substrates using dc magnetron sputtering of graphite or graphite/copper targets. The local density of electron states was determined from normalized differential tunneling conductance with the aim of probing the individual sp ²-phase clusters. The well-defined valence-band edge and the varying (i.e., dependent on the scanning coordinate) shape of the distribution of the density of electron states within the conduction band are characteristic of the a-C:H films; also, the largest experimental value of the band gap in these films is ～3 eV; finally, the tendency towards the stable position of the Fermi level at a level of ～1 eV above the valence-band top is observed in a-C:H films. The a-C:(H, Cu) films are homogeneous with respect to the local density of electron states, which is accounted for by the formation of a homogeneous surface layer in the course of growth.     

用PECVD法沉积α-C:H薄膜的研究

本文报导了使用PECVD方法沉积的α-C:H溥膜的工艺条件、薄膜结构和物性之间的联系。指出,α-C:H膜中石墨和金刚石成分的比值密切相关于反应气氛CH_4/(CH_4+H_2)的比例以及沉积系统中的衬底温度和施加在平行板电极之间的直流偏压。最后,利用化学反应平衡方程讨论了α-C:H膜的沉积机理以及[H]基对生成膜结构的影响。     

使用ECR苯等离子体沉积含氢非晶碳薄膜

用苯作工作气体。在一个电子回旋共振（ＥＣＲ）微波等离子体化学气相沉积系统中制备了含氢非晶碳膜（ａ－Ｃ：Ｈ）．对苯等离子体作了质谱分析,发现苯分解后形成的主要基团是Ｃ２Ｈ４等,而不是常规甲烷放电的ＣＨ３。这将影响膜的结构。实验中还考察了沉积参数,如功率、气压、流量、基片温度对膜的沉积速率的影响。实验表明：沉积速率随微波功率、气压和流量的增加而上升;随温度的升高先升后降,存在极值,对制备的膜作了氢含量     

a-SiC/c-Si异质结太阳能电池中a-SiC:H薄膜的设计分析

通过应用Scharfetter-Gummel解法数值求解Poisson方程,对热平衡p (a-SiC:H）/n(c-Si）异质结太阳能电池进行计算机数值模拟分析。给出了p (a-SiC:H）膜厚及其p型掺杂浓度设计,还讨论了p (a-SiC:H)/n(c-Si）异质结太阳能电池稳定性。     

Current-voltage characteristics of electroluminescent Me/(a-Si:H):Er/c-Si structures prepared by magnetron sputtering

Current-voltage characteristics of electroluminescent structures composed of metal, erbium-doped amorphous silicon, and crystalline silicon and prepared by magnetron sputtering were measured and analyzed. It is shown that the carrier transport in a high-resistivity (a-Si:H):Er film (resistivity ～10⁹ Ω cm) proceeds by the mechanism of unipolar-injection space-charge-limited currents controlled by two types of traps. Trap parameters, namely, the densities and ionization energies of acceptor and donor centers (～10¹⁹ cm^?3 for both types of traps; 0.85–0.95 eV and 0.4 eV, respectively) are estimated by analyzing the current-voltage characteristics. In the light of the results obtained, the published excitation mechanism of erbium-related electroluminescence in such a material is discussed.     

p-n heterojunctions

A classical kinetic emission model coupled with an assumed energy band diagram which includes the effects of a discontinuity in the electron affinity, effective mass, permittivity and the energy gap at the junction interface is used as the basis for an analysis of the static current-voltage characteristic of the abrupt p-n heterojunction. The derived characteristic is then used to determine regions of quasi-equilibrium within the depletion layer and to predict the position dependence of the quasi-Femri levels.

Two distinct modes of operation are predicted for the heterojunctions I–V characteristic: Metal-semiconductor type operation where the current is limited by the ability of the carriers to surmount the potential barrier at the junction interface and homojunction type operation where the current is limited by the ability of the carriers to diffuse away from the junction depletion region. The predicted extrapolated saturation current for the former type of operation, is in general, significantly less than that for the latter. The position dependence of the quasi-Fermi levels is also different for the two types of operation. For metal-semiconductor type operation a drop in the quasi-Fermi level across the depletion layer is expected, whereas for homodiode type operation there is a negligible variation of the quasi-Fermi level in this region.

The heterojunction I–V characteristic presented here, which differs significantly from previous models, agrees favourably with experimental data on Ge-GaAs heterojunctions reported in the literature and with others recently fabricated by the present authors.     

Absorption and the optical gap of a-C:H films produced from acetylene plasmas

Films of amorphous hydrogenized carbon (a-C:H) are prepared by chemical vapor deposition using a dc glow discharge. The absorption is studied over wavelengths of 400–2400 nm. Two Gaussian-like bands are identified with peaks at ∼600 and ∼800 nm. The ratio of the integrated intensities of these bands (I ₆₀₀/I ₈₀₀) is found to decrease as the voltage is raised. The changes in the ratio I ₆₀₀/I ₈₀₀ are compared with the variation in the fundamental Raman scattering bands in order to clarify the nature of the visible absorption in the a-C:H films. Two simple schemes for transparent insulating films with E _T ⩾1.5 eV and for “black” conducting a-C:H films with E _T ⩽1 eV are proposed for explaining the relationship between the structure of the absorption edge and the width of the Tauc gap (E _T ). Fiz. Tekh. Poluprovodn. 33, 469–475 (April 1999)     

Hydrogenated amorphous-silicon/crystalline-silicon heterojunctions:properties and applications

Fundamental properties of amorphous-silicon/crystalline-silicon heterojunctions are studied through their capacitance-voltage and current-voltage characteristics. In light of the heterojunction properties, the applicability to devices such as vidicon targets, gamma-ray detectors, solar cells, and heterojunction bipolar transistors is discussed     

Photosensitive Ox/GaAs heterojunctions: Creation and properties

A method for the thermal oxidation of GaAs crystals in air is suggested and the first photosensitive Ox/n-GaAs heterojunctions, where Ox is a native oxide, are fabricated. The steady current-voltage characteristics and spectra of relative quantum efficiency of the new structures are studied. The features of the spectra of photoactive absorption of the obtained heterojunctions are discussed. The potential of using vacuumfree thermal oxidation of the GaAs crystals in air to fabricate broadband heterophotoconverters of optical radiation on their basis is established.     

掺胺碳膜及其对甲酸蒸气传感特性

用射频等离子体化学沉积方法制备氢化非晶碳（a-C:H)膜。在等离子体气氛中引入胺基团,则能够在a-C:H薄膜沉积过程中将胺基团掺入薄膜的网络结构中。喇曼光谱表明薄膜具有无序态结构。红外分析表明薄膜中有胺基团存在,将掺胺a－C：H薄膜作为质量传感膜沉积到石英晶体表面制成气相质量传感器。测试表明掺胺a－C：H膜对甲酸蒸气具有高的响应灵敏度,好的线性相关系数和线性响应范围。     

Transport properties and photosensitivity of metal/porous-silicon/c-Si structures

The current-voltage characteristics, photosensitivity, and impedance of p-type Al/porous-silicon/c-Si structures with 0.2 to 6-μm-thick porous layers of 80% porosity are studied. It is shown that at reverse and small forward bias voltages the current is determined by the potential barrier of the c-Si substrate at the isotypic porous-silicon/c-Si heterojunction. The photosensitivity is determined by the absorption of light in the c-Si substrate. The potential barrier of the metal/porous-silicon contact does not influence the photosensitivity or the currentvoltage characteristics of the structures. The experimental plots of the dependence of the impedance on applied forward bias, thickness of porous silicon layer, and frequency agree well with the theoretical dependences, if an equivalent circuit including two RC circuits connected in series and comprised of the resistance and geometric capacitance of the porous silicon layer and the resistance and capacitance of the potential barrier of the c-Si substrate is used. Fiz. Tekh. Poluprovodn. 33, 211–214 (February 1999)     

Photoelectric properties of n-CdS/p-InP heterojunctions

The polarization method for studying photoactive absorption is used to investigate the photoconversion processes in CdS/InP heterojunctions as a function of the orientation of the indium phosphide substrate. The results of these investigations demonstrate the sensitivity of the photoelectric processes to several factors, including the crystallographic orientation of the p-type InP substrate and the optical quality of the CdS layer. The induced photopleochroism coefficient of these heterojunctions increases proportionally to the square of the angle of incidence (P _I ∼Θ²). Such CdS/InP heterojunctions can be employed as polarization-photosensitive devices. Fiz. Tekh. Poluprovodn. 32, 72–77 (January 1998)     

Electrical properties of anisotype heterojunctions n-CdZnO/p-CdTe

Anisotype surface-barrier n-Cd_0.5Zn_0.5O/p-CdTe heterojunctions are fabricated by the high-frequency sputtering of a Cd_0.5Zn_0.5O alloy film onto a freshly cleaved single-crystal CdTe surface. The main electrical properties of the heterojunctions are studied and the dominant mechanisms of charge transport are established, namely, the multistage tunnel-recombination mechanism under forward bias, Frenkel-Pool emission, and tunneling under forward bias. The influence of the surface electrically active states at the heterojunction interface is analyzed and their surface concentration is evaluated: N _ss ?? 10¹⁴ cm^?2.