SiC based Si/SiC heterojunction and its rectifying characteristics

The Si on SiC heterojunction is still poorly understood, although it has a number of potential applications in electronic and optoelectronic devices, for example, light-activated SiC power switches where Si may play the role of an light absorbing layer. This paper reports on Si films heteroepitaxially grown on the Si face of （0001） n-type 6H-SiC substrates and the use of B2H6 as a dopant for p-Si grown at temperatures in a range of 700-950℃. X-ray diffraction （XRD） analysis and transmission electron microscopy （TEM） tests have demonstrated that the samples prepared at the temperatures ranged from 850℃ to 900℃ are characterized as monocrystalline silicon. The rocking XRD curves show a well symmetry with FWHM of 0.4339° Omega. Twin crystals and stacking faults observed in the epitaxial layers might be responsible for widening of the rocking curves. Dependence of the crystal structure and surface topography on growth temperature is discussed based on the experimental results. The energy band structure and rectifying characteristics of the Si/SiC heterojunctions are also preliminarily tested.

Indium–tin oxide films obtained by DC magnetron sputtering for improved Si heterojunction solar cell applications

The indium-tin oxide （ITO） film as the antireflection layer and front electrodes is of key importance to obtaining high efficiency Si heterojunction （HJ） solar cells. To obtain high transmittance and low resistivity ITO films by direct-current （DC） magnetron sputtering, we studied the impacts of the ITO film deposition conditions, such as the oxygen flow rate, pressure, and sputter power, on the electrical and optical properties of the ITO films. ITO films of resistivity of 4 x 10-4 ~.m and average transmittance of 89% in the wavelength range of 380-780 nm were obtained under the optimized conditions： oxygen flow rate of 0.1 sccm, pressure of 0.8 Pa, and sputtering power of 110 W. These ITO films were used to fabricate the single-side HJ solar cell without an intrinsic a-Si：H layer. However, the best HJ solar cell was fabricated with a lower sputtering power of 95 W, which had an efficiency of 11.47%, an open circuit voltage （Voc） of 0.626 V, a filling factor （FF） of 0.50, and a short circuit current density （Jsc） of 36.4 mA/cm2. The decrease in the performance of the solar cell fabricated with high sputtering power of 110 W is attributed to the ion bombardment to the emitter. The Voc was improved to 0.673 V when a 5 nm thick intrinsic a-Si：H layer was inserted between the （p） a-Si：H and （n） c-Si layer. The higher Voc of 0.673 V for the single-side HJ solar cell implies the excellent c-Si surface passivation by a-Si：H.

Forward and reverse electron transport properties across a CdS/Si multi-interface nanoheterojunction

The electron transport behavior across the interface plays an important role in determining the performance of op- toelectronic devices based on heterojunctions. Here through growing CdS thin film on silicon nanoporous pillar array, an untraditional, nonplanar, and multi-interface CdS/Si nanoheterojunction is prepared. The current density versus voltage curve is measured and an obvious rectification effect is observed. Based on the fitting results and model analyses on the forward and reverse conduction characteristics, the electron transport mechanism under low forward bias, high forward bias, and reverse bias are attributed to the Ohmic regime, space-charge-limited current regime, and modified Poole-Frenkel regime respectively. The forward and reverse electrical behaviors are found to be highly related to the distribution of inter- facial trap states and the existence of localized electric field respectively. These results might be helpful for optimizing the preparing procedures to realize high-performance silicon-based CdS optoelectronic devices.

Rectification and electroluminescence of nanostructured GaN/Si heterojunction based on silicon nanoporous pillar array

A GaN/Si nanoheterojunction is prepared through growing Ga N nanocrystallites（nc-GaN） on a silicon nanoporous pillar array（Si-NPA） by a chemical vapor deposition（CVD） technique at a relatively low temperature. The average size of nc-Ga N is determined to be ~10 nm. The spectral measurements disclose that the photoluminescence（PL） from GaN/SiNPA is composed of an ultraviolet（UV） band and a broad band spanned from UV to red region, with the feature that the latter band is similar to that of electroluminescence（EL）. The electron transition from the energy levels of conduction band and, or, shallow donors to that of deep acceptors of Ga N is indicated to be responsible for both the broad-band PL and the EL luminescence. A study of the I-V characteristic shows that at a low forward bias, the current across the heterojunction is contact-limited while at a high forward bias it is bulk-limited, which follows the thermionic emission model and space-charge-limited current（SCLC） model, respectively. The bandgap offset analysis indicates that the carrier transport is dominated by electron injection from n-GaN into the p-Si-NPA, and the EL starts to appear only when holes begin to be injected from Si-NPA into GaN with biases higher than a threshold voltage.

A Novel Ideal Ohmic Contact SiGeC/Si Power Diode with Graded Doping Concentration

A novel structure of ideal ohmic contact p^＋ （SiGeC）-n^- -n^＋ diodes with three-step graded doping concentration in the base region is presented, and the changing doping concentration gradient is also optimized. Using MEDICI, the physical parameter models applicable for SiGeC/Si heterojunction power diodes are given. The simulation results indicate that the diodes with graded doping concentration in the base region not only have the merit of fast and soft reverse recovery but also double reverse blocking voltage,and their forward conducting voltage has dropped to some extent,compared to the diodes with constant doping concentration in the base region. The new structure achieves a good trade-off in Qs-Vf-Ir ,and its combination of properties is superior to ideal ohmic contact diodes and conventional diodes.

Ge/Si heterojunction L-shape tunnel field-effect transistors with hetero-gate-dielectric

A Ge/Si heterojunction L-shaped tunnel field-effect transistor combined with hetero-gate-dielectric （GHL-TFET） is proposed and investigated by TCAD simulation. Current-voltage characteristics, energy-band diagrams, and the distri- bution of the band-to-band tunneling （BTBT） generation rate of GHL-TFET are analyzed. In addition, the effect of the vertical channel width on the ON-current is studied and the thickness of the gate dielectric is optimized for better suppression of ambipolar current. Moreover, analog/RF figure-of-merits of GHL-TFET are also investigated in terms of the cut-off frequency and gain bandwidth production. Simulation results indicate that the ON-current of GHL-TFET is increased by about three orders of magnitude compared with that of the conventional L-shaped TFET. Besides, the introduction of the hetero-gate-dielectric not only suppresses the ambipolar current effectively but also improves the analog/RF performance drastically. It is demonstrated that the maximum cut-off frequency of GHL-TFET is about 160 GHz, which is 20 times higher than that of the conventional L-shaped TFET.

Temperature-dependent rectifying and photovoltaic characteristics of an oxygen-deficient Bi_2Sr_2Co_2O_y/Si heterojunction

A Bi2Sr2Co2Oy/Si heterojunction is obtained by growing a layer of p-type oxygen-deficient Bi2Sr2Co2Oy film on a commercial n-type silicon wafer by pulsed laser deposition. Its rectifying and photovoltaic properties are studied in a wide temperature range from 20 K to 300 K. The transport mechanism under the forward bias can be attributed to a trap- filled space-charge-limited current conduction mechanism. Under the irradiation of a 532-nm continuous wave laser, a clear photovoltaic effect is observed and the magnitude ofphotovoltage increases as the temperature decreases, The results demonstrate the potential application of a Bi2SrzCo2Oy-based heterojunction in the photoelectronic devices.

Novel Si/SiC heterojunction lateral double-diffused metal-oxide semiconductor field-effect transistor with p-type buried layer breaking silicon limit

A novel silicon carbide(SiC) on silicon(Si) heterojunction lateral double-diffused metal-oxide semiconductor fieldeffect transistor with p-type buried layer(PBL Si/SiC LDMOS) is proposed in this paper for the first time.The heterojunction has breakdown point transfer(BPT) characteristics,and the BPT terminal technology is used to increase the breakdown voltage(BV) of Si/SiC LDMOS with the deep drain region.In order to further optimize the surface lateral electric field distribution of Si/SiC LDMOS with the deep drain region,the p-type buried layer is introduced in PBL Si/SiC LDMOS.The vertical electric field is optimized by Si/SiC heterojunction and the surface lateral electric field is optimized by the p-type buried layer,which greatly improves the BV of device and alleviates the relationship between BV and specific on-resistance(R_(on,sp)).Through TCAD simulation,when the drift region length is 20 μm,the BV is significantly improved from 249 V for the conventional Si LDMOS to 440 V for PBL Si/SiC LDMOS,increased by 77%;And the BV is improved from 384 V for Si/SiC LDMOS with the deep drain region to 440 V for the proposed structure,increased by 15%.The figure-of-merit(FOM) of the Si/SiC LDMOS with the deep drain region and PBL Si/SiC LDMOS are 4.26 MW/cm^(2) and 6.37 MW/cm^(2),respectively.For the PBL Si/SiC LDMOS with the drift length of 20 μm,the maximum FOM is 6.86 MW/cm^(2).The PBL Si/SiC LDMOS breaks conventional silicon limit.

Interfacial photoconductivity effect of type-Ⅰ and type-Ⅱ Sb2Se3/Si heterojunctions for THz wave modulation

An in-depth understanding of the photoconductivity and photocarrier density at the interface is of great significance for improving the performance of optoelectronic devices. However, extraction of the photoconductivity and photocarrier density at the heterojunction interface remains elusive. Herein, we have obtained the photoconductivity and photocarrier density of 173 nm Sb2Se3/Si(type-Ⅰ heterojunction) and 90 nm Sb2Se3/Si(type-Ⅱ heterojunction) utilizing terahertz(THz) time-domain spectroscopy(THz-TDS) and a theoretical Drude model. Since type-Ⅰ heterojunctions accelerate carrier recombination and type-Ⅱ heterojunctions accelerate carrier separation, the photoconductivity and photocarrier density of the type-Ⅱ heterojunction(21.8×10^(4)S·m^(-1),1.5 × 10^(15)cm^(-3)) are higher than those of the type-Ⅰ heterojunction(11.8×10^(4)S·m^(-1),0.8×10^(15)cm^(-3)). These results demonstrate that a type-Ⅱ heterojunction is superior to a type-Ⅰ heterojunction for THz wave modulation. This work highlights THz-TDS as an effective tool for studying photoconductivity and photocarrier density at the heterojunction interface. In turn, the intriguing interfacial photoconductivity effect provides a way to improve the THz wave modulation performance.

CdS/Si nanofilm heterojunctions based on amorphous silicon films:Fabrication,structures,and electrical properties

Shortening the distance between the depletion region and the electrodes to reduce the trapped probability of carriers is a useful approach for improving the performance of heterojunction.The CdS/Si nanofilm heterojunctions are fabricated by using the radio frequency magnetron sputtering method to deposit the amorphous silicon nanofilms and Cd S nanofilms on the ITO glass in turn.The relation of current density to applied voltage(I-V)shows the obvious rectification effect.From the analysis of the double logarithm I-V curve it follows that below~2.73 V the electron behaviors obey the Ohmic mechanism and above~2.73 V the electron behaviors conform to the space charge limited current(SCLC)mechanism.In the SCLC region part of the traps between the Fermi level and conduction band are occupied,and with the increase of voltage most of the traps are occupied.It is believed that Cd S/Si nanofilm heterojunction is a potential candidate in the field of nano electronic and optoelectronic devices by optimizing its fabricating procedure.

The Effects of Fabrication Prameters and Electroforming Phenomenon on CdTe/Si (p) Heterojunction Photovoltaic Solar Cell

The In-doped CdTe/Si (p) heterostruture was fabricated and its electrical and photoelectrical properties were studied and interpreted. During the fabrication processes of CdTe/Si heterojunction, some practical troubles were encountered. However, the important one was the formation of the SiO2 thin oxide layer on the soft surface of the Si during the formation of the back contact. The silicon wafer was subjected to different chemical treatments in order to remove the thin oxide layer from the silicon wafer surfaces. It was found that the heterojunction with Si (p+) substrate gave relatively high open circuit voltage comparing with that of Si (p) substrate. Also an electroforming phenomenon had been observed in this structure for the first time which may be considered as a memory effect. It was observed that there are two states of conduction, non-conducting state and conducting state. The normal case is the non-conducting state. As the forward applied voltage increased beyond threshold value, it switches into the conducting state and remains in this state even after the voltage drops to zero.

a-Si/c-Si heterojunction solar cells on SiSiC ceramic substrates

Silicon thin-film solar cells are considered to be one of the most promising cells in the future for their potential advantages, such as low cost, high efficiency, great stability, simple processing, and none-pollution. In this paper, latest progress on poly-crystalline silicon solar cells on ceramic substrates achieved by our group was reported. Rapid thermal chemical vapor deposition (RTCVD) was used to deposited poly-crystalline silicon thin films, and the grains of as-grown film were enlarged by Zone-melting Recrystallization (ZMR). As a great change in cell′s structure, traditional diffused pn homojunction was replaced by a-Si/c-Si heterojunction, which lead is to distinct improvement in cell′s efficiency. A conversion efficiency of 3.42% has been achieved on 1 cm2 a-Si/c-Si heterojunction solar cell (Isc=16.93 mA, Voc=310.9 mV, FF=0.6493, AM=1.5 G, 24 ℃), while the cell with diffused homojunction only got an efficiency of 0.6%. It indicates that a-Si emitter formed at low temperature might be more suitable for thin film cell on ceramics.

Simulation of a-Si:H/c-Si heterojunction solar cells: From planar junction to local junction

In order to obtain higher conversion efficiency and to reduce production cost for hydrogenated amorphous silicon/crystalline silicon(a-Si:H/c-Si) based heterojunction solar cells, an a-Si:H/c-Si heterojunction with localized p–n structure(HACL) is designed. A numerical simulation is performed with the ATLAS program. The effect of the a-Si:H layer on the performance of the HIT(heterojunction with intrinsic thin film) solar cell is investigated. The performance improvement mechanism for the HACL cell is explored. The potential performance of the HACL solar cell is compared with those of the HIT and HACD(heterojunction of amorphous silicon and crystalline silicon with diffused junction) solar cells.The simulated results indicate that the a-Si:H layer can bring about much absorption loss. The conversion efficiency and the short-circuit current density of the HACL cell can reach 28.18% and 43.06 m A/cm^2, respectively, and are higher than those of the HIT and HACD solar cells. The great improvement are attributed to(1) decrease of optical absorption loss of a-Si:H and(2) decrease of photocarrier recombination for the HACL cell. The double-side local junction is very suitable for the bifacial solar cells. For an HACL cell with n-type or p-type c-Si base, all n-type or p-type c-Si passivating layers are feasible for convenience of the double-side diffusion process. Moreover, the HACL structure can reduce the consumption of rare materials since the transparent conductive oxide(TCO) can be free in this structure. It is concluded that the HACL solar cell is a promising structure for high efficiency and low cost.

SiGeC/Si功率二极管的数值模拟与分析

将SiGeC技术应用于功率半导体器件的特性改进,提出了一种新型p+(SiGeC)n-n+异质结功率二极管结构.在分析SiGeC合金材料物理特性的基础上,给出了该结构的关键物理参数模型,并在此基础上利用MEDICI模拟,对比分析了C的引入对器件各种电特性的影响.此外,还模拟比较了不同p+区厚度对器件反向漏电流的影响.结果表明:在SiGe/Si功率二极管中加入少量的C,在基本不影响器件正向I V特性和反向恢复特性的前提下,大大减少了器件的反向漏电流,并且C的加入还减小了器件特性对材料临界厚度的依赖性,提高了器件稳定性.

SiGeC异质结功率二极管通态特性研究

研究了一种大功率低功耗p+(SiGeC)-n--n+异质结二极管结构,分析了Ge、C含量对器件正向通态特性的影响。结果表明:与常规的Si p-i-n二极管相比,在正向电流密度不超过1000 A/cm2情况下,p+(SiGeC)-n--n+二极管的正向压降有明显的降低。当电流密度为10 A/cm2时,Si p-i-n二极管的压降为0.655 V,而SiGeC异质结二极管的压降只有0.525 V,大大降低了器件的通态功耗。在相同正向电流密度的条件下,SiGeC异质结二极管在n-区存储的载流子比Si二极管的减少了1个数量级以上,这导致前者的关断时间远小于后者。

非掺杂型Si/SiGe异质结外延与表征

以自旋为编码单元的硅基半导体量子计算与传统微电子工艺兼容,易拓展且可以同位素纯化提高退相干时间,因而备受关注.本研究工作通过分子束外延生长了高质量非掺杂型Si/SiGe异质结并测试了二维电子气迁移率.球差电镜观察到原子级尖锐界面,原子力显微镜表征显示其表面均方根粗糙度仅为0.44 nm,低温下迁移率达到20.21×10^(4)cm^(2)·V^(–1)·s^(–1).不同栅压下载流子浓度和迁移率的幂指数为1.026,材料丁格比值在7—12之间,表明载流子主要受到背景杂质散射和半导体/氧化物的界面散射.

Sensitivity investigation of 100-MeV proton irradiation to SiGe HBT single event effect

The single event effect(SEE) sensitivity of silicon–germanium heterojunction bipolar transistor(Si Ge HBT) irradiated by 100-Me V proton is investigated. The simulation results indicate that the most sensitive position of the Si Ge HBT device is the emitter center, where the protons pass through the larger collector-substrate(CS) junction. Furthermore, in this work the experimental studies are also carried out by using 100-Me V proton. In order to consider the influence of temperature on SEE, both simulation and experiment are conducted at a temperature of 93 K. At a cryogenic temperature, the carrier mobility increases, which leads to higher transient current peaks, but the duration of the current decreases significantly.Notably, at the same proton flux, there is only one single event transient(SET) that occurs at 93 K. Thus, the radiation hard ability of the device increases at cryogenic temperatures. The simulation results are found to be qualitatively consistent with the experimental results of 100-Me V protons. To further evaluate the tolerance of the device, the influence of proton on Si Ge HBT after gamma-ray(^(60)Coγ) irradiation is investigated. As a result, as the cumulative dose increases, the introduction of traps results in a significant reduction in both the peak value and duration of the transient currents.

Si基热氧化Si_(1-x-y)Ge_xC_y薄膜的室温光致发光特性

采用等离子体增强化学气相淀积 ( PECVD)法在 Si( 1 0 0 )衬底上淀积一层厚度约为1 70 nm的富 Ge高 C含量的 Si1- x- y Gex Cy 薄膜 ,然后将其分别在 80 0℃和 1 1 0 0℃下湿氧氧化2 0 min.在室温下观测到强烈的光致发光 .室温下的光致发光谱 ( PL谱 )测量显示 ,80 0℃下氧化后的样品在 370 nm和 396nm附近有两个光致发光带 ,1 1 0 0℃下氧化后的样品只在 396nm附近有一个光致发光带 .396nm附近的发光带可归之于由氧化薄膜中的缺陷 O- Si- O ( Si02 )或 O- Ge-O( Ge02 )引起的 ,而 370 nm附近的发光带与薄膜中 Ge-