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.     

等离子刻蚀a-Si:H/a-C:H超晶格

本文介绍了 C_yF_(14)+ O_2等离子刻蚀 a=Si:H/a-C:H 超晶格的工艺原理及方法,简便可行.     

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.     

Analysis of light-induced degradation mechanisms in α-Si:H/μc-Si:H solar photovoltaics

The photoinduced degradation of the i-α-Si:H layer in tandem photovoltaic converters based on α-Si:H/μc-Si:H structures is analyzed in terms of the “H-collision-” and “floating-bond” models and modifications of these. It is shown that the form of the degradation dependence is well described by all models under consideration. Compared with the modified models, the original “H-collision-” and “floating-bond” models yield estimates for saturated dangling-bond concentrations, which are always dependent on the intensity of the light that caused the degradation. The modified “floating-bond” model makes it possible to exclude this dependence, and the modified “H-collision” model describes the occurrence of this dependence in a certain range of illumination intensities and its absence in another range, which is in best agreement with experimental 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.     

Absorption and photoconductivity of boron-compensated μc-Si:H

A study is reported of absorption, conductivity, and photoconductivity of photosensitive μc-Si:H weakly doped with boron. The dependences of photoconductivity on the temperature and the intensity of light were measured in a temperature range of 100–400 K for photon energies of 0.9, 1.3, and 1.8 eV. The results obtained are explained by the dominant contribution of the microcrystalline phase and the states at the interfaces of microcrystals to the transport and recombination of nonequilibrium carriers in μc-Si:H. Possible recombination mechanisms and the change of their role with temperature are analyzed.     

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     

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。     

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。     

异质结硅太阳能电池a—Si：H薄膜的研究

通过应用Scharfetter-Gummel数值求解Poisson方程，对热平衡态P^ （a-Si:H)/n(c-Si)异质结太阳能电池进行计算机数值模拟分析。结果指出，采用更薄P^ (a-Si：H）薄膜设计能有效增强光生载流子的传输与收集，从而提高a-Si/c-Si异质结太阳能电池的性能。同时，还讨论了P^ (a-Si:h)薄膜中P型掺杂浓度对光生载流了传输与收集的影响。高强茺光照射下模拟，计算表明，a-Si/c-Si异质结结构太阳能电池具有较高光稳定性。     

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.     

Voltage-tunable SiO2-isolated a-SiC:H and/or a-SiN:H p–i–n thin-film LEDs fabricated on c-Si

A voltage-tunable amorphous p–i–n thin-film light emitting diodes (TFLEDs) with SiO₂-isolation on n⁺-type crystalline silicon (c-Si) has been proposed and fabricated successfully. The structure of the device with i-a-SiC:H and i-a-SiN:H luminescent layers is indium–tin–oxide (ITO)/p⁺-a-Si:H/p⁺-a-SiC:H/i-a-SiC:H/i-a-SiN:H/n⁺-a-SiCGe: H/n⁺-a-SiC:H/n⁺-c-Si/Al. This device revealed a brightness of 695 cd/m² at an injection current density of 300 mA/cm². Its EL (electroluminescence) peak wavelength exhibited blue-shift from 655 to 565 nm with applied forward-bias (V) increasing from 15 to 19 V, but the EL peak wavelength was red-shifted from 565 to 670 nm with further increase of V from 19 to 23 V. By comparing with the EL spectra from p–i–n TFLEDs with i-a-SiC:H or i-a-SiN:H luminescent layer only, the EL spectrum of this TFLED could consist of three bands of radiations from the tail-to-tail-state recombinations in (1) i-a-SiC:H layer, (2) i-a-SiN:H layer, and (3) i-a-SiC:H/p⁺-a-SiC:H junction.     

Photoelectric phenomena in (μc xa1−x )-Si:H/c-Si heterostructures

Heterostructures (μc _xa_1−x )-Si:H/c-Si with a various volume fraction x of microcrystalline and amorphous Si phases were obtained by plasmochemical deposition. The fraction variation was achieved by changing the silane content in H₂. The steady-state current-voltage characteristics and spectral dependences of photosensitivity of the structures obtained were investigated. The latter dependences were recorded by exposing the samples to the natural and linearly polarized light in relation to the phase composition of thin (d ₁ ≅ 0.6–0.8 μm) films of microcrystalline and amorphous Si. The photovoltaic effect and induced photopleochroism of the structures obtained were detected. The prospects of using a new type of heterojunction in photoconverters of natural and linearly polarized light were assessed. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 11, 2001, pp. 1316–1319. Original Russian Text Copyright ? 2001 by Mell, Nikolaev, V. Rud’, Yu. Rud’, Terukov.     

含氢非晶碳膜(a-C:H)红外光学特性的研究

采用端部霍尔离子源在硅基底上制备了含氢非晶碳膜（a-C:H）,并测量了4 000~1 500 cm-1的红外透射光谱。基于单层薄膜的透射关系,获得了仅有六个拟合参数的光学常数计算模型。利用该模型,可以同时获得薄膜在宽波段范围内的光学常数和厚度:折射率的最大值为1.94,消光系数的最大值为0.014 9,拟合薄膜厚度为617 nm 。     

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.