Theoretical investigation of efficiency of a p-a-SiC:H/i-a-Si:H/n-μc-Si solar cell

A solar cell with a novel structure is investigated by means of the analysis ofmicroelectronic and photonic structure (AMPS). The power conversion efficiency is investigated with the variations in interface recombination ve-locity, thicknesses of p-type layer, intrinsic layer, n-type layer, and doping density. Results show that it is available and preferable in theory to employ a-SiC:H as a window layer in p-a-SiC:H/i-a-Si:H/n-μc-Si solar cells, and provide a new approach to improving the power conversion efficiency of amorphous silicon solar cells.     

Electroluminescence characteristics and current-conductionmechanism of a-SiC:H p-i-n thin-film light-emitting diodes with barrierlayer inserted at p-i interface

In order to improve the electroluminescence (EL) characteristics of the hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diode (TFLED), a barrier layer (BL) was inserted at its p-i interface to enhance the hole injection efficiency under forward-bias operation. The a-SiC:H TFLED's with various optical gaps of BL had been fabricated and characterized. In addition, a composition-graded n⁺-layer was used to reduce its series and contact resistances to the Al electrode and hence the EL threshold voltage (V_th) of an a-SiC:H BL TFLED. The highest obtainable brightness of an a-SiC:H BL TFLED was 342 cd/m² at an injection current density of 600 mA/cm² and the lowest EL V _th achievable was 6.0 V. The current-conduction mechanism of an a-SiC:H BL TFLED had also been investigated. Within the lower applied-bias region, it showed an ohmic current, while within the higher applied-bias region, a space-charge-limited current (SCLC) was observed     

An amorphous SiC/Si two-color detector

A glass/ITO/(n⁺-i) a-SiC:H/(p⁺-i-n⁺) a-Si:H/A1 photodetector with a voltage-selectable spectral response was fabricated successfully. It consists of two back-to-back p-i-n junctions, including an a-SiC:H/a-Si:H heterojunction and a-Si:H homojunction. As the bias at the ITO side changes from 2 to -2 V, the responsivity to light with a wavelength of 6000 Å increases 18 times, whereas for light of 4500 Å, it decreases three times. The detectivity ratio at these two wavelengths then changes from 0.16 to 4 which provides a good distinction between two colors, i.e., orange and blue.     

Characteristics of MSM photodetectors with trench electrodes onp-type Si wafer

U-grooved metal-semiconductor-metal photodetectors (UMSM-PD's) having various trench depths of interdigitated electrodes and an intrinsic hydrogenated amorphous silicon (i-a-Si:H) to c-Si heterojunction have been fabricated successfully on a p-type [100] Si wafer. The U-grooved structures on c-Si were achieved with a simple orientation-dependent etching (ODE) process. Some important characteristics of the obtained UMSM-PDs are presented and discussed. An UMSM-PD with a 70 nm i-a-Si:H overlayer, 1.45 μm-deep recessed electrodes, and 3 μm finger width and spacing, had a full width at half maximum (FWHM) of 50.6 ps and a full-time of 132 ps for its temporal response under a bias of 15 V. The significant improvements of transient response for UMSM-PD, as compared to the conventional one, were attributed to the trench electrodes resulted in a stronger lateral electric field in the light absorption region of photodetector. At a bias of 20 V, this UMSM-PD had a responsivity of 0.25 A/W as measured with an 0.83-μm incident semiconductor laser, a high photo/dark current ratio about 2000, and an internal quantum efficiency of 36%. This high photo/dark current ratio would be due to the additional i-a-Si:H overlayer on Si wafer. These mentioned performances were much better than those of the conventional Si-based planar MSM-PD     

Reducing dark current in a high-speed Si-based interdigitated trench-electrode MSM photodetector

The authors have studied higher dark-current temperature dependence in a trench-electrode Si-based metal-semiconductor-metal (MSM) photodetector which has a hydrogenated intrinsic amorphous silicon (i-a-Si:H) dark-current suppression layer. The poor dark-current temperature-dependence performance could be improved significantly by reducing the number of trap states in the depletion region of the reverse-biased crystalline/amorphous Si heterojunction. To reduce the trap states, a modified plasma-enhanced chemical vapor deposition (PECVD) system, which reduced the ion bombardment on the Si substrate, was employed to deposit an i-a-Si:H layer. Moreover, since fewer trap states in a photodetector will result in a degradation of the fall time of the temporal response of the device, a Ti electrode, which has a lower Schottky barrier height (0.62 eV) than that (0.84 eV) of the previous Cr electrode used with i-a-Si:H, was employed for compensation. The device obtained exhibited very good dark-current stability and temporal response. The dark current only increased from 6 to 34 nA, when the operating temperature was increased from room temperature (R. T.) to 57/spl deg/C, much lower than that of the previously reported 3-V bias voltage one (from 22 to 209 nA). Device responsivity and quantum efficiency also showed obvious improvement, both at R. T. (0.192 A/W and 0.29) and 57/spl deg/C (0.213 A/W and 0.32, respectively) and were higher than those previously reported (0.174 A/W and 0.26, at 57/spl deg/C).     

A metal-amorphous silicon-germanium alloy Schottky barrier forinfrared optoelectronic IC on glass substrate application

The effects of material and structure parameters on an amorphous-silicon-germanium alloy Schottky barrier diode's responsivity have been investigated in detail. The effects contradict each other. A compromise is made in selecting parameters for construction of a Si_1-xGe_x:H Schottky barrier for an IR detector. The optimized amorphous-silicon-germanium alloy Schottky diode using x=0.43 alloy with a 900-nm-thick i-layer was found to have a peak at 850 nm with a responsivity of 0.6 A/W under -2-V bias. The diode also has a response time of 33 μs and slight photodegradation. Thus, the diode becomes a candidate for manufacturing the infrared OEIC (optoelectronic integrated circuit) on glass substrate in applications which require size, reproducibility, and low cost more than sensitivity     

Amorphous Silicon 16—bit Array Photodetector^①

An amorphous silicon 16-bit array photodetector with the a-SiC/a -Si heterojunction diode is presented. The fabrication processes of the device were studied systematically. By the optimum of the diode structure and the preparation procedures, the diode with Id< 10 -12 A/mm2 and photocurrent Ip^0.35 A/W has been obtained at the wavelength of 632 nm.     

0.34 THz肖特基二极管高速OOK信号直接检波器

为了满足340 GHz高速OOK无线通信的需求,完成了340 GHz零偏置波导检波器的设计、加工和测试。首先,在高频电磁仿真软件HFSS中对准垂直结构二极管（QVD）进行建模仿真,并结合二极管的非线性模型确定二极管的阻抗;随后设计了输入波导-微带转换以及低通滤波器等无源结构,并同时对二极管进行阻抗匹配;最后进行了检波器的加工和测试。测试结果表明该检波器的电压灵敏度在334 GHz时最佳,最大值为2 210 V/W,并且在315 GHz~357 GHz频率范围内的典型值为1 400 V/W,其对应的等效噪声功率典型值为5 pW Hz-0.5。最后,还利用该检波器进行了340 GHz频段的高速OOK信号接收实验,结果表明,该检波器能够近乎无误地检测10 Gbps的OOK信号,并且在OOK信号速率为15 Gbps时,检波器解调得到的误码率为3.1510-7,证明了该检波器的高速信号检测能力能够满足高速OOK无线通信系统的需求。     

a-SiC:H/pin势阱结构可见光注入式电致发光(英文)

a-SiC:H/pin势阱结构可见光注入式电致发光(英文)@朱冰$中国科技大学 @陈培力$宁波大学 @白贵儒$宁波大学     

A p-silicon nanowire/n-ZnO thin film heterojunction diode prepared by thermal evaporation

This paper represents the electrical and optical characteristics of a SiNW/ZnO heterojunction diode and subsequent studies on the photodetection properties of the diode in the ultraviolet （UV） wavelength region. In this work, silicon nanowire arrays were prepared on p-type （100）-oriented Si substrate by an electroless metal deposition and etching method with the help of ultrasonication. After that, catalyst-free deposition of zinc oxide （ZnO） nanowires on a silicon nanowire （SiNW） array substrate was done by utilizing a simple and cost-effective thermal evaporation technique without using a buffer layer. The SEM and XRD techniques are used to show the quality of the as-grown ZnO nanowire film. The junction properties of the diode are evaluated by measuring current-voltage and capacitance-voltage characteristics. The diode has a well-defined rectifying behavior with a rectification ratio of 190 at -t-2 V, turn-on voltage of 0.5 V, and barrier height is 0.727 eV at room temperature under dark conditions. The photodetection parameters of the diode are investigated in the bias voltage range of ± 2 V. The diode shows responsivity of 0.8 A/W at a bias voltage of 2 V under UV illumination （wavelength = 365 nm）. The characteristics of the device indicate that it can be used for UV detection applications in nano-optoelectronic and photonic devices.     

Flexible Transparent ZnO:Al/ZnO/CuAlO x :Ca Heterojunction Diodes on Polyethylene Terephthalate Substrates

Transparent flexible n ⁺-ZnO:Al (100 nm)/n-ZnO (40 nm)/p-CuAlO _x :Ca (100 nm, 200 nm, 300 nm) diodes were fabricated on polyethylene terephthalate substrates at room temperature using a sputtering technique. No additional heat treatment was performed on the fabricated devices. Increase of the diode layer thickness reduced the on-current and leakage-current levels simultaneously, which led the rectification ratio to first increase and then decrease as the p-layer thickness increased. The ultraviolet (UV) response of the diode was also investigated under irradiation at 365 nm. The n ⁺-ZnO:Al (100 nm)/n-ZnO (40 nm)/p-CuAlO _x :Ca (200 nm) diode exhibited photocurrent/leakage current ratio of 1.03 × 10³ and responsivity of 0.64 A/W at reverse bias of ?6 V when measured in flat status. The corresponding photocurrent/leakage current ratio and responsivity were 7.99 × 10² and 0.65 A/W, respectively, for an outwardly bent diode with 5.5 cm radius of curvature. The increases of current levels under bending are attributed to the decreases of series resistance for the diode under tensile strain.     

Optimization of Al/a-SiC:H optical sensor device by means of thermal annealing

The optimization of optoelectronic properties of Al/a-SiC:H Schottky diodes grown as Al/a-SiC:H/c-Si(n) structures is studied by means of thermal annealing of a-SiC:H thin films. According to the spectral response of the Schottky diodes the measured quantum efficiency, η_measured, increases with increasing annealing temperature (400–600 °C), whereas η_measured decreases for T_a>600 °C. For T_a=600 °C, optimum material quality of a-SiC:H films is achieved and the spectral response of the Al/a-SiC:H/c-S(n) structures present very high and almost constant values (η_measured80%) for the whole range of wavelengths from 500 up to 850 nm. These results show that our Al/a-SiC:H/c-S(n) structures can be very attractive as optical sensors. Diffusion length calculations as well as the mobility by lifetime product (μτ)_p of the minority carriers (holes) of a-SiC:H films present a dependence on T_a similar to that of the measured quantum efficiency. Finally, the quantum efficiency of films processed with T_a=675 °C is found to increase when the Al/a-SiC:H/c-S(n) structures are exposed to hydrogen, a result that could be promising for the construction of a hydrogen detection sensor.     

The role of an amorphous SiC:H `buffer' in the high-performanceμc-SiC:H/a-SiC:H/poly-Si heterojunction solar cells

High-efficiency solar cells have been developed using relatively simple processing at low temperatures up to 300°C. The cells studied were p⁺ μc-SiC:H/p a-SiC:H (buffer)/n poly-Si and n⁺ μc-SiC:H/n a-SiC:H (buffer)/p poly-Si heterojunctions fabricated by the electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) method. The thin amorphous buffer layer played an important role in improving the photovoltaic performance. The optimization of the buffer layer thickness resulted in a conversion efficiency of η=15.4% under AM1 solar simulated radiation of 100 mW/cm²     

An amorphous SiC:H emitter heterojunction bipolar transistor

After confirming the successful application of the amorphous SiC:H(a-SiC:H)/crystalline Si(c-Si) heterostructure in a solar cell and considering its prospective application in Bi-CMOS devices, an attempt has been made to apply the same in the fabrication of a heterojunction bipolar transistor. A p-n-p heterojunction bipolar transistor with a wide band-gap boron-doped amorphous SiC:H emitter and crystalline Si (base, collector) has been realized and is reported here for the first time. Good device performance has been observed at the a-SiC:H deposition temperature of 450°C. Preliminary results gave a current gain,h_{FE(max)}) of 50 at a current density of approximately 2.4 A/cm²(base dose 2 × 10¹²/cm², width ≃ 0.4 µm). Temperature dependence of the transistorh_{FE}-I_{C}characteristics was also studied.     

Silicon matrix disorder in amorphous hydrogenated silicon alloys

The authors report a detailed investigation of correlations between Urbach energies from photothermal deflection spectroscopy and Raman half-widths of transverse optic (TO)-like Si-Si modes as a measure of silicon matrix disorder in glow-discharge amorphous hydrogenated silicon (a-Si:H) and a-SiGe:H, as well as in glow-discharge and sputtered a-SiC:H and a-SiN:H. A corresponding decrease in TO full width at half-maximum (FWHM) and Urbach energy E₀ for soft deposition techniques yields bond angle distributions as narrow as 8.5° for the best a-Si:H films. Even at the lowest levels of nitrogen incorporation, simultaneous increases in E₀ and TO-like half-widths indicate that lattice distortions occur due to threefold coordination of nitrogen in the a-Si:H matrix. In contrast, no deviation of silicon TO-FWHM could be detected in a-SiC:H of up to 35 at.% of carbon content, whereas Urbach edges broaden in a well-known manner that is interpreted in terms of -CH₃ incorporation into the amorphous network. Diborane doping and sputter deposition, however, give rise to lattice distortions in a-SiC:H, which reflects changes in the carbon coordination     

High-speed Si-based metal-semiconductor-metal photodetectors with an additional composition-graded i-a-Si1−xGex:H layer

The response-speed of Si-based metal-semiconductor-metal (MSM) photodetectors was improved by depositing a composition-graded intrinsic hydrogenated amorphous silicon–germanium (i-a-Si_1−xGe_x:H) layer on crystalline silicon (c-Si). In contrast to the non-composition-graded one (using intrinsic hydrogenated amorphous silicon (i-a-Si:H) layer), the full width at half maximum (FWHM) and fall time of the photodetector transient response were improved from 145.2, 404.6 to 107.6, 223.4 ps respectively. The experimental results showed that the device responsivity and quantum efficiency were increased from 0.329 (A/W) and 0.492 to 0.414 and 0.619 respectively by the employed composition-graded technique. We propose that this enhancement is due to a smoother barrier that is formed at the c-Si and i-a-Si_1−xGe_x:H interface. A lower deposition temperature of i-a-Si_1−xGe_x:H layer could be used to further reduce the fall time of the device transient response from 315.6 (250 °C) to 97.6 (180 °C) ps. To improve the contact properties between Cr electrode and i-a-Si_1−xGe_x:H layer, an annealing technique in hydrogen ambient was employed. The device knee voltage, which is the applied voltage at which the device current start to enter the saturation region in its current (log-scale) versus applied voltage characteristics, could be reduced to around 3.5 V after annealing.     

A DIL-type miniature optical transceiver module using an InGaAsPhalf-transmittance photodiode for TCM optical access networks

A compact DIL-type miniature optical transceiver module has been developed without using a conventional 3 dB optical coupler. This transceiver is composed of a newly designed InGaAsP half-transmittance photodiode (HT-PD) and a 1.3-μm multiquantum-well laser diode (MQW-LD). An HT-PD is used both as a photodetector and as a window for laser diode (LD) light. Fiber output power of 0 dBm at the drive current of 33.8 mA and responsivity of 0.58 A/W at the reverse-voltage of 2 V were obtained. The fundamental characteristics of the HT-PD are studied and discussed     

温度和电场对a-SiC; H TFLED发光亮度的影响

通过载流子注入和复合输运模型 ,分析比较了温度和电场对 pin注入型非晶硅碳薄膜发光二极管 (a -SiC :HTFLED)发光亮度的影响。分析表明发光有源i层内大电场尤其是大电流引起的高温度决定着大电流下二极管的发光亮度。     

两种结构GaN基太阳盲紫外探测器

分别在金属有机化学汽相沉积（MOCVD）生长的i-Al0.33Ga0.67N／AlN／n-GaN和p-Al0.45Ga0．55N／i—Al0.45Ga0.55N／n＋-Al0.65Ga0.35N的异质结构上，成功研制了太阳盲区的肖特基型和PIN型紫外探测器。研究结果表明，Au与i—Al0.33Ga0.67N形成了较好的肖特基结，响应波长从250—290nm，峰值（286nm）响应率约为0．08A／W；PIN型紫外探测器的响应波长从230～275nm，峰值（246nm）响应率约为0．02A／W。     

硅紫外光敏管设计研究

本文讨论了光吸收系数、掺杂浓度、掺杂浓度分布、表面反射等各种因素对硅光敏管紫外响应的影响。提出了制作硅紫外光敏管的设计原则:浅结、低掺杂、高表面浓度梯度和 SiO_2层满足消反射条件。并具体分析了一个实例。