Effects of annealing on the performance of 4H-SiC metal–semiconductor–metal ultraviolet photodetectors

4H-SiC-based metal–semiconductor–metal (MSM) photodetectors (PDs) have been designed, fabricated, and characterized, in which nickel Schottky contacts were needed. Current–voltage and spectral responsivity measurements were carried out at room temperature to character the effect of annealing on the performance of the MSM devices. It was found to improve both Schottky barrier height and ideality factors after annealing at appropriate temperature. The chemical component depth profiles of XPS measurement showed nickel silicides were produced at the interface, leading to improvement of the Ni/4H-SiC contacts and the performance of the PDs. The MSM PDs with RTA had a lower dark current (0.45 pA at 5 V bias voltage), a typical responsivity of 0.094 A/W at 20 V and displayed peak response wavelength at 290 nm.     

Simulation and optimization of a 6H-SiC metal-semiconductor-metal ultraviolet photodetector

正Based on thermionic emission theory,a model of a 6H-SiC metal-semiconductor-metal(MSM) ultraviolet photodetector is established with the simulation package ISE-TCAD.A device with 3μm electrode width(W) and 3μm electrode spacing(L) is simulated.The findings show that the MSM photodetector has quite a low dark current of 15 pA at 10V bias and the photocurrent is two orders of magnitude higher than the dark current.The influences of different structures on dark and illuminated current-voltage characteristics of the MSM photodetector are investigated to optimize the device parameters.Simulation results indicate that the maximum photocurrent and the highest ratio of photocurrent to dark current at 15 V bias are 5.3 nA and 327 with device parameters of W=6μm,L=3μm and W =3μm,L=6μm,respectively.     

Simulation and optimization of a 6H-SiC metal-semiconductor-metal ultraviolet photodetector

Based on thermionic emission theory,a model of a 6H-SiC metal-semiconductor-metal (MSM) ultraviolet photodetector is established with the simulation package ISE-TCAD.A device with 3μm electrode width (W) and 3μm electrode spacing (L) is simulated.The findings show that the MSM photodetector has quite a low dark current of 15 pA at 10 V bias and the photocurrent is two orders of magnitude higher than the dark current.The influences of different structures on dark and illuminated current-voltage characteristics of the MSM photodetector are investigated to optimize the device parameters.Simulation results indicate that the maximum photocurrent and the highest ratio of photocurrent to dark current at 15 V bias are 5,3 nA and 327 with device parameters of W = 6μm,L=3μm and W =3μm,L = 6μm,respectively.     

Spatial nonuniformity of 4H-SiC avalanche photodiodes at high gain

We report spatial nonuniformity of responsivity of 4H-SiC avalanche photodiodes at high gain (M > 1000) that results from variation in the doping density. Two-dimensional raster scans show a steady decline laterally across the device. The direction in which the spatial response decreases is the same as that of increasing breakdown voltage on the wafer.     

AlGaN solar-blind Schottky photodiodes fabricated on 4H-SiC

Solar-blind AlGaN-based Schottky photodiodes grown on 4H-SiC substrate are reported. The fabricated devices demonstrate dark current density as low as 2.2/spl times/10/sup -10/ A/cm/sup 2/ at a reverse bias of 5 V. A zero-bias peak responsivity of 44 mA/W was achieved at 256 nm, corresponding to an external quantum efficiency of 21%. Under a low illumination power density of 10 nW/cm/sup 2/, a rejection ratio of more than two orders of magnitude was observed in the wavelength range from 270 to 310 nm. A room-temperature solar-blind detectivity of 7.9/spl times/10/sup 14/ cm/spl middot/Hz/sup 1/2/W/sup -1/ was estimated at 256 nm under zero bias.     

Effects of rapid thermal annealing on nitrided gate oxide grown on 4H-SiC

The electrical characteristics of thermally nitrided gate oxides on n-type 4H-SiC, with and without rapid thermal annealing processes, have been investigated and compared in this paper. The effects of annealing time (isothermal annealing) and annealing temperature (isochronal annealing) on the gate oxide quality have also been systematically investigated. After rapid isothermal and isochronal annealings, there has been a significant increase in positive oxide-charge density and in oxide-breakdown time. A correlation between the density of the positive oxide charge and the oxide breakdown reliability has been established. We proposed that the improvement in the oxide-breakdown reliability, tested at electric field of 11 MV/cm, is attributed to trapping of injected electron by the positive oxide charge and not solely due to reduction of SiC-SiO₂ interface-trap density.     

Effect of annealing temperature on the electrical characteristics of Platinum/4H-SiC Schottky barrier diodes

Pt/4H-SiC Schottky barrier diodes have been fabricated to investigate the effect of annealing on the electrical characteristics of the fabricated devices. The parameters such as barrier height, ideality factor and donor concentration were deduced from the current–voltage (I–V) and the capacitance–voltage (C–V) measurements at room temperature. Diodes showed non-ideal behaviour like high value of ideality factor and lower value of barrier height. A barrier height of 1.82?eV was obtained from C–V measurements and it was 1.07?eV when obtained from the I–V measurements with ideality factor 1.71 for as-deposited diodes at room temperature. The diodes, therefore, were annealed in the temperature range from 25°C to 400°C to observe the effect of annealing temperature on these parameters. Schottky barrier height and ideality factors were found to be temperature-dependent. After rapid thermal annealing upto 400°C, a barrier height of 1.59?eV from C–V measurements and the value of 1.40?eV from I–V measurements with ideality factor 1.12 were obtained. Barrier heights deduced from C–V measurements were consistently larger than those obtained from I–V measurements. To come to terms with this discrepancy, we re-examined our results by including the effect of ideality factor in the expression of the barrier height. This inclusion of ideality factor results in reasonably good agreement between the values of barrier height deduced by the above two methods. We believe that these improvements in the electrical parameters result from the improvement in the quality of interfacial layer.     

Two-dimensional numerical computation of the structure-dependent spectral response in a 4H-SiC metal-semiconductor-metal ultraviolet photodetector with consideration of reflection and absorption on contact electrodes

A two-dimensional model of a 4H-SiC metal-semiconductor-metal(MSM) ultraviolet photodetector has been established using a self-consistent numerical calculation method.The structure-dependent spectral response of a 4H-SiC MSM detector is calculated by solving Poisson’s equation,the current continuity equation and the current density equation.The calculated results are verified with experimental data.With consideration of the reflection and absorption on the metal contacts,a detailed study involving various electrode heights(H),spacings (S) and widths(W) reveals conclusive results in device design.The mechanisms responsible for variations of responsivity with those parameters are analyzed.The findings show that responsivity is inversely proportional to electrode height and is enhanced with an increase of electrode spacing and width.In addition,the ultraviolet (UV)-to-visible rejection ratio is > 103.By optimizing the device structure at 10 V bias,a responsivity as high as 180.056 mA/W,a comparable quantum efficiency of 77.93%and a maximum UV-to-visible rejection ratio of 1875 are achieved with a detector size of H = 50 nm,S =9μm and W = 3μm.     

Study of reverse dark current in 4H-SiC avalanche photodiodes

Temperature-dependent current-voltage (I-V) measurements have been used to determine the reverse dark current mechanisms in 4H-SiC avalanche photodiodes (APDs). A pn junction vertical mesa structure, passivated with SiO/sub 2/ grown by plasma enhanced chemical vapor deposition, exhibits predominate leakage current along the mesa sidewall. Similar APDs, passivated by thermal oxide, exhibit lower dark current before breakdown; however, when the temperature is higher than 146/spl deg/C, an anomalous dark current, which increases rapidly with temperature, is observed. This current component appears to be eliminated by the removal of the thermal oxide. Near breakdown, tunneling is the dominant dark current mechanism for these pn devices. APDs fabricated from a pp/sup -/n structure show reduced tunneling current. At room temperature, the dark current at 95% of breakdown voltage is 140 fA (1.8 nA/cm/sup 2/) for a 100-/spl mu/m diameter APD. At a gain of 1000, the dark current is 35 pA (0.44 /spl mu/A/cm/sup 2/).     

碲镉汞探测器在高温目标下的光电倍增效应

针对不同波段的碲镉汞红外探测器在探测高温目标情况下的特性进行了研究。测量结果显示随着所探测目标温度的不断升高,器件光生电流亦随之上升,但并非平行变化,这就导致了探测器动态微分阻抗不断下降。器件微分电阻下降的主要原因是p?蛳n结由于背景辐照和反向偏压的增加,引起光生载流子的激增,碰撞电离导致的光电倍增效应引起的,这种效应使得器件光生电流并非是单纯叠加在器件反偏暗电流之上、只随辐射通量而变化的变量,同时也是偏压的函数,随着偏压的增大会对微分阻抗有一个降低作用。通过理论计算这种假设得到了证实,实验结果和理论计算吻合的比较好。     

Visible blind p-i-n ultraviolet photodetector fabricated on 4H-SiC

The 4H-SiC visible blind p-i-n ultraviolet (UV) photodetector has been designed, fabricated and characterized. The dark I-V characteristics of the detector were carried out at room temperature. It was found that the photocurrent of detector was at least two orders of magnitude higher than the dark current. The photon response spectrum of the detector was measured and calibrated. The ratio of responsivity at 275 nm to that at 375 nm was nearly 100, which implied that the photodetector has a great improved visible blind performance.     

Investigation of the reliability of 4H-SiC MOS devices for high temperature applications

In this paper, the excellent reliability of 4H-SiC MOS devices during high temperature operation is demonstrated for a gate oxide processed in N₂O. A temperature dependent Fowler-Nordheim analysis is used to show that statistical energy spreading accounts for only part of the reported temperature induced barrier height degradation. Poole-Frenkel current caused by acceptor like traps in the oxide due to carbon interstitials is proposed to be responsible for the additional current observed. Temperature and electric field acceleration of the time to dielectric breakdown is investigated at elevated temperatures in order to predict the expected MOS lifetime during high temperature operation.     

4H-SiC p-i-n紫外光电探测器的电容-电压特性研究

分析并比较了4H-SiC p-i-n紫外光电探测器的电容-电压（C-V）特性随温度和偏置电压的变化情况,观测到4H-SiC p-i-n结构中的深能级缺陷。结果表明：由于近零偏压时探测器i型层已处于耗尽状态,其高频（1 MHz）C-V特性几乎不随反向偏压变化,随着温度升高,被热离化的自由载流子数量增多导致高频结电容随之增大;探测器的低频（100 kHz）结电容比高频结电容具有更强的电压和温度依赖性,原因在于被深能级缺陷俘获的载流子随反向偏压增大或随温度升高而被离化,从而对结电容产生影响。     

4H-SiC MESFET频率特性研究

研究了4H-SiCMESFET的频率特性与器件几何及物理参数的关系。发现常温300K时,4H-SiCMESFET的截止频率随沟道掺杂浓度增加而上升;随沟道厚度的增加而降低;随栅长的增加而下降;随工作温度的增加变化很小,500K以上时略有降低。300K下,在沟道掺杂为4×1017cm-3、沟道厚度为0.25mm、栅长0.30mm、栅压偏置为-5V时,模拟得到的截止频率fT达到18.62GHz,显示该器件在高频、高温、大功率领域的极大优越性和应用前景。     

一氧化氮退火对高温氧化SiC/SiO2界面特性的影响研究

本文研究了高温（1300℃）氧化并在一氧化氮（NO）气体中进行氧化后退火方法对4H-SiC 金属-氧化物-半导体（MOS）电容的SiC/SiO2界面特性的影响,主要通过SiC MOS的电容-电压(C-V)特性详细讨论了NO退火时间和温度与SiO2/SiC界面特性的相互关系. 结果表明在NO气体中进行氧化后退火可明显降低界面态密度,并且界面态密度随着温度和时间的增加会进一步降低。 同时,与常规1200℃及以下氧化温度相比,1300℃下热生长的氧化层具有更低的界面态密度且显著缩短了氧化时间,节约了生产成本。     

Effect of annealing temperature on 1.5 μm photoluminescence from Er-lmplanted 6H-SiC

The effect of post-implantation anneal on erbium-doped 6H-SiC has been investigated. 6H-SiC has been implanted with 330 keV Er⁺ at a dose of 1 × 1013 /cm2. Er depth profiles were obtained by secondary ion mass spectrometry (SIMS). The as-implanted Er-profile had a peak concentration of∼1.3 × 10¹⁸/cm³ at a depth of 770Å. The samples were annealed in Ar at temperatures from 1200 to 1900°C. The photoluminescence intensity integrated over the 1.5 to 1.6 μm region is essentially independent of annealing temperature from 1400 to 1900°C. Reduced, but still significant PL intensity, was measured from the sample annealed at 1200°C. The approximate diffusivity of Er in 6H SiC was calculated from the SIMS profiles, yielding values from 4.5 × 10⁻¹⁶ cm²/s at 1200°C to 5.5 × 10⁻¹⁵ cm²/s at 1900°C.     

退火温度对高介电常数Ta2O5薄膜电学性能的影响

利用磁控溅射法在硅(Si)衬底上沉积了Ta2O5薄膜,对薄膜进行了不同温度的退火处理,并利用X射线衍射仪对薄膜的微观结构进行了分析.然后在Si的背面和介电薄膜的上面沉积Pt电极,组成了金属—氧化物—半导体( MOS)电容器,对不同温度下退火得到的薄膜制备的MOS电容器的电学性能进行了研究.结果表明,薄膜在700℃开始结...     

Effect of rapid thermal annealing on the current-voltage characteristics of 4H-SiC Schottky diodes

The effect of rapid thermal annealing (temperature 600–800°C; duration 2 min) on the forward current-voltage characteristics of 4H-SiC Schottky diodes is studied. Tungsten, nickel, chromium, and molybdenum deposited by electron-beam sputtering in vacuum are used as the Schottky-contact metals. Dissimilar types of influence exerted by the thermal treatment on the barrier height and scatter of the contact parameters, which characterize the degree of their uniformity, are found for different metals.     

Effects of high temperature annealing and laser irradiation on activation rate of phosphorus

Thermal annealing and laser irradiation were used to study the activation rate of phosphorus in silicon after ion implantation. The activation rate refers to the ratio of activated impurity number to the total impurity number in the sample. After injecting phosphorus with the dose and energy (energy = 55 keV, dose = 3 × 10¹⁵ cm^–2), the samples were annealed at different temperatures, and laser irradiation experiments were performed after annealing. The experimental results showed that the activation rate of phosphorus was the highest at 850 °C, and the highest activation rate was 67%. Upon femtosecond laser irradiation samples after thermal annealing, while keeping the crystalline silicon surface without damage, the activation rate was improved. When the energy-flux density of the femtosecond laser was 0.65 kJ/cm², the activation rate was the highest, increasing from 67% to 74.81%.