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。     

Nonlinearity of p-i-n photodetectors

At higher operating frequencies, the field dependence of the carrier velocity in p-i-n photodetectors generates harmonics and intermodulation products that can degrade the dynamic range of RF fiber-optic links. The authors present both a perturbational theory and measured harmonic data for a p-i-n photodiode operated at very high power densities which show that this and other detector nonlinear effects need not seriously compromise link performance. In particular, neither transit-time nor static nonlinearities in p-i-n photodiodes need limit the dynamic range of fiber-optic links operating below 5 GHz. The fact that the theoretical bandwidth of the photodiode, with all parasitic capacitance and inductance ideally removed, is 17 GHz, suggests that comparable spur-free performance should be achievable at X and Ku-band frequencies, once packaging parasitics are reduced     

Low-loss, high-voltage 6H-SiC epitaxial p-i-n diode

The p-i-n diodes were fabricated using 31 /spl mu/m thick n/sup -/- and p-type 6H-SiC epilayers grown by horizontal cold-wall chemical vapor deposition (CVD) with nitrogen and aluminum doping, respectively. The diode exhibited a very high breakdown voltage of 4.2 kV with a low on-resistance of 4.6 m/spl Omega/cm/sup 2/. This on-resistance is lower (by a factor of five) than that of a Si p-i-n diode with a similar breakdown voltage. The leakage current density was substantially lower even at high temperatures. The fabricated SiC p-i-n diode showed fast switching with a turn-off time of 0.18 /spl mu/s at 300 K. The carrier lifetime was estimated to be 0.64 /spl mu/s at 300 K, and more than 5.20 /spl mu/s at 500 K. Various characteristics of SiC p-i-n diodes which have an advantage of lower power dissipation owing to conductivity modulation were investigated.     

Comparison of GaN p-i-n and Schottky rectifier performance

The performance of GaN p-i-n and Schottky rectifiers fabricated on the same wafer was investigated as a function of device size and operating temperature. There was a significant difference in reverse breakdown voltage (490 V for p-i-n diodes; 347 V for the Schottky diodes) and forward turn-on voltage (~5 V for the p-i-n diodes; ~3.5 V for the Schottky diodes). Both types of device showed a negative temperature coefficient for reverse breakdown, with value -0.34±0.05 V·K^-1     

Silicon p-i-n photodetectors with integrated transistor amplifiers

A novel silicon photodetector is presented, incorporating transistor gain in a p-i-n photodiode and its performance is analyzed. Gain and noise power frequency characteristics are analytically derived in terms of an equivalent circuit. These analytical results are in good agreement with experimental results. Noise power is estimated and it is shown that, in the video frequency range, the S/N ratio is far superior to that of APD for relatively large signal levels. Detector operational features are described.     

Electron and hole traps in GaN p-i-n photodetectors grown by reactive molecular beam epitaxy

GaN p-i-n photodetectors grown on sapphire by reactive molecular beam epitaxy have been characterized by measurements of room-temperature current-voltage (I-V), temperature-dependent capacitance (C-V-T), and deep level transient spectroscopy (DLTS) under both majority and minority carrier injection. Due to what we believe to be threading dislocations, the reverse I-V curves of p-i-n photodetectors show typical electric-field enhanced soft breakdown characteristics. A carrier freeze-out due to the de-ionization of Mg-related deep acceptors has been found by C-V-T measurements. Three electron traps, B (0.61 eV), D (0.23 eV), and E₁ (0.25 eV) and one hole trap, H₃ (0.79 eV) have been revealed by DLTS measurements. The photodetectors with lower leakage currents usually show higher responsivity and lower trap densities of D and E₁.     

Characteristics of GaN grown on 6H-SiC with different AlN buffers

Characteristics of GaN grown on 6H-SiC (0001) substrates using different thicknesses of AlN buffers are studied. It is found that the surface morphology and crystal quality of GaN film closely depends on the strain state of the AlN buffer. For a thicker AlN buffer, there are cracks on GaN surface, which make the GaN films unsuitable for applications. While for a thinner AlN buffer, more dislocations are produced in the GaN film, which deteriorates the performance of GaN. Possible generation mechanisms of cracks and more dislocations are investigated and a ～100 nm AlN buffer is suggested to be a better choice for high quality GaN on SiC.     

Speed and efficiency in multiple p-i-n photodetectors

We present a theoretical evaluation of the application of multiple intrinsic layers to enhancing the quantum efficiency of high-speed p-i-n photodetectors. It is shown that the use of multiple layers may lead to substantial improvements in the efficiency of detectors operating in the 20-100-GHz range, provided that the device area is reduced to limit the intrinsic capacitance and special care is taken to avoid large parasitic effects. Potential fabrication schemes are discussed     

Interfacial effects during GaN growth on 6H-SiC

GaN growth on 6H-SiC was investigated for heterojunction device applications. Dopant diffusion and surface reactions were discovered at the GaN/SiC heterojunction. A systematic study was therefore conducted focusing on: 1) SiC substrate preparation, 2) SiC nitridation; the effect of flowing ammonia (NH₃) at 1050°C on the SiC, and 3) the conductivity type and carrier concentration of the SiC substrate. Atomic force microscopy measurements revealed that the SiC substrates became smoother after the nitridation process possibly due to nitrogen chemisorption and etching. Current-voltage and capacitance-voltage measurements on Cr-Schottky diodes made on SiC revealed evidence for an increased potential barrier in the nitrided samples that can be explained by an interfacial monolayer ofSiN_x. Furthermore, we compared GaN/SiC heterojunction n-n and n-p diodes made from direct and selective GaN growth. Capacitancevoltage measurements on GaN/SiC n-p heterojunctions indicate that the effective doping in the junction increases as the growth temperature increases. Secondary ion mass spectrometry measurements exposed a tail of Al in the GaN due to acceptor out-diffusion from the p-SiC.     

6H-SiC衬底上采用不同厚度AlN缓冲层对GaN外延层的影响

采用不同厚度AlN作为缓冲层在6H-SiC衬底上生长了GaN外延层,并利用X射线衍射,拉曼散射和透射电子显微镜等对GaN性质进行了研究。AlN缓冲层的应变状态对GaN的晶体质量和表面形貌有很大影响。较厚的AlN缓冲层会导致GaN表面出现裂纹,而太薄的AlN缓冲层会导致GaN层较高的位错密度,从而恶化器件性能。分析了GaN产生裂纹和高位错密度的机制,并采用较优厚度（100nm）的AlN缓冲层生长出高质量的GaN外延层。     

Nonlinear saturation behaviors of high-speed p-i-n photodetectors

We present numerical simulations of the ultrafast transport dynamics in an ultrahigh-speed double-heterostructure p-i-n photodetector. Nonlinear saturation behaviors under high field and high power illumination are investigated with the external circuit response considered. Damping constants and diffusion constants are both treated as electric-field- and carrier-concentration dependent in our model in order to take into account the effect of carrier scattering. We have also considered the carrier trapping at the heterostructure interfaces for the first time. Besides the drift-induced space charge screening effect, we find that saturation of external circuit and carrier-trapping-induced screening effect are also the dominant mechanisms contributed to the nonlinear bandwidth reduction under high power illumination. On the other hand, previously reported plasma oscillations are found to be greatly suppressed by including strong carrier diffusion effect in the model     

GaN基p-i-n结构紫外光探测器

用反应分子束外延(RMBE)方法在蓝宝石衬底上制备了GaN p-i-n结构,应用常规的半导体工艺制成了紫外光探测器,测试结果显示其正向导通电压为4.6 V,反向击穿电压大于40 V;室温下反偏3 V时的暗电流为6.68 pA,峰值响应度0.115 A/W出现在367 nm处;400 nm处的响应度为6.59×10-5A/W,比峰值响应度低四个量级.     

Large-signal response of p-i-n photodetectors using short pulses with small spot sizes

In this paper, the response of a surface-normal p-i-n photodetector that was incorporated in an optically controlled optical gate was analyzed using short-pulsed, high-energy optical inputs with small spot sizes. Simulation results based in part on diffusive conduction were compared against the experimental data, providing an understanding of the device response. Results also demonstrated that p-i-n photodetectors may be designed so that reducing the spot size, counterintuitively, results in negligible additional field screening.     

Microwave p-i-n diodes and switches based on 4H-SiC

The 4H-SiC p-i-n diodes were designed, fabricated, and characterized for use in microwave applications. The diodes with mesa structure diameters between 80 and 150 /spl mu/m, exhibited a blocking voltage of 1100 V, a 100-mA differential resistance of 1-2 /spl Omega/, a capacitance below 0.5 pF at a punchthrough voltage of 100 V and a carrier effective lifetime between 15-27 ns. X-band microwave switches based on 4H-SiC p-i-n diodes are demonstrated for the first time. The switches exhibited insertion loss as low as 0.7 dB, isolation up to 25 dB and were able to handle microwave power up to 2.2 kW in isolation mode and up to 0.4 kW in insertion mode.     

Current-voltage characteristics of GaN and AlGaN p-i-n diodes

The current-voltage characteristics of GaN and Al_0.08Ga_0.92N p-i-n diodes were investigated. The experimental p-i-n structures were grown by MOCVD on 6H-SiC with Si and Mg as dopants. The i region was formed by simultaneously doping with donor and acceptor impurities during growth. Analysis of the current-voltage characteristics showed that current flow in the p-i-n diodes is due to either drift of thermally excited holes or electron-hole recombination in the i region via impurity centers—just as predicted by the Ashley-Milnes theory. These impurity centers are attributed to Mg acceptor levels. Fiz. Tekh. Poluprovodn. 32, 369–372 (March 1998)     

高性能背照式GaN/AlGaN p-i-n紫外探测器的制备与性能

研究了GaN/AlGaN异质结背照式P-i-n结构可见盲紫外探测器的制备与性能.GaN/MGaN外延材料采用金属有机化学气相沉积(MOCVD)方法生长,衬底为双面抛光的蓝宝石,缓冲层为AiN,n型层采用厚度为0.8 μm的Si掺杂Al0.3Ga0.7形成窗口层,i型层为0.18 μm的非故意掺杂的GaN,P型层为0.15 μm的Mg掺杂GaN.采用C12、Ar和BCl3感应耦合等离子体刻蚀定义台面,光敏面面积为1.96×10-3cm2.可见盲紫外探测器展示了窄的紫外响应波段,响应区域为310-365 nm,在360 nm处响应率最大,为0.21 A/W,在考虑表面反射时,内量子效率达到82%;优质因子R0A为2.00×108 Ω·cm2,对应的探测率D*=2.31×1013·Hz1/2·W-1;且零偏压下的暗电流为5.20×10-13A.     

GaN MSM UV photodetectors with titanium tungsten transparent electrodes

GaN metal-semiconductor-metal (MSM) ultraviolet photodetectors with titanium tungsten (TiW) transparent electrodes were fabricated and characterized. It was found that the 10-nm-thick TiW film deposited with a 300-W RF power can still provide a reasonably high transmittance of 75.1% at 300 nm, a low resistivity of 1.7/spl times/10/sup -3/ /spl Omega//spl middot/cm and an effective Schottky barrier height of 0.773 eV on u-GaN. We also achieved a peak responsivity of 0.192 A/W and a quantum efficiency of 66.4% from the GaN ultraviolet MSM photodetector with TiW electrodes. With a 3-V applied bias, it was found that minimum noise equivalent power and maximum D/sup */ of our detector were 1.987/spl times/10/sup -10/ W and 6.365/spl times/10/sup 9/ cmHz/sup 0.5/W/sup -1/, respectively.     

Nitride-Based ultraviolet metal-semiconductor-metal photodetectors with a low-temperature GaN layer

The GaN metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors with a low-temperature (LT)-GaN layer have been demonstrated. It was found that we could achieve a two orders of magnitude smaller, photodetector-dark current by introducing a LT-GaN layer, which could be attributed to the larger Schottky-barrier height between the Ni/Au metal contact and the LT-GaN layer. It was also found that photodetectors with the LT-GaN layer could provide a larger photocurrent to dark-current contrast ratio and a larger UV-to-visible rejection ratio. The maximum responsivity was found to be 3.3 A/W and 0.13 A/W when the photodetector with a LT-GaN layer was biased at 5 V and 1 V, respectively.     

Tunable superlattice p-i-n photodetectors: characteristics, theory,and application

Extended measurements and theory on the recently developed monolithic wavelength demultiplexer consisting of voltage-tunable superlattice p-i-n photodetectors in a waveguide confirmation are discussed. It is shown that the device is able to demultiplex and detect two optical signals with a wavelength separation of 20 nm directly into different electrical channels at a data rate of 1 Gb/s and with a crosstalk attenuation varying between 20 and 28 dB, depending on the polarization. The minimum acceptable crosstalk attenuation at a data rate of 100 Mb/s is determined to be 10 dB. The feasibility of using the device as a polarization angle sensor for linearly polarized light is also demonstrated. A theory for the emission of photogenerated carriers out of the quantum wells is included, since this is potentially a speed limiting mechanism in these detectors. It is shown that a theory of thermally assisted tunneling by polar optical phonon interaction is able to predict emission times consistent with the observed temporal response