金属-半导体-金属(MSM)结构4H-SiC紫外光电探测器的研制

MSM结构探测器具有结构与工艺简单、制备成本低、量子效率高等特点而在探测器应用中得到重视。本文制备了采用镍作为肖特基接触形成的MSM4H—SiC紫外光电探测器，并测量和分析了在不同的偏压下其光电特性。结果表明，该探测器的暗电流非常小，在偏压为15V的时候，漏电流密度约为70nA／cm^2，光电流比暗电流高约2个数量级，其光谱响应表明，其最高光谱响应与380nm的比值约为1000倍，说明该探测器具有良好的紫外可见比。     

GaN MSM photodetectors with photo-CVD annealed Ni/Au electrodes

Thin Ni/Au (3/6 nm) bi-layer metal films annealed by photo-chemical vapor deposition (photo-CVD) were investigated. With proper annealing in oxygen by the photo-CVD systems, it was found that the transmittance of the deposited Ni/Au increased from 67 to 85% in the region between 350 and 450 nm. GaN metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors with photo-CVD annealed Ni/Au contact electrodes were also fabricated. It was found that dark current of the detector became significantly smaller after annealing. With a 1 V applied bias, it was found that we can achieve a photocurrent to dark current contrast ratio of 2.54×10³ from the photodetectors with 600 °C photo-CVD annealed Ni/Au contacts.     

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.     

SiO2钝化膜对非极性AlGaN-MSM紫外探测器的影响

采用SiO₂钝化膜方法对引入低温AlN插入层的高 温MOCVD外延生长的未掺杂的非极性AlGaN外 延薄膜制备了金属-半导体-金属(MSM)结构的紫外光电探测器。研究了磁控溅射SiO₂钝 化膜对探测器光电性能的提 升。暗电流测试表明,钝化处理使探测器的暗电流可以降低了2-3个数量级。在5V偏压下 , 通过光谱响应测试发现,经过钝化处理的探测器在300 nm处具有陡峭 的截止边,具有很好 的深紫外特性,光谱响应范围提高了3个数量级,抑制比高达10⁵。     

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.     

High-Detectivity Nitride-Based MSM Photodetectors on InGaN–GaN Multiquantum Well With the Unactivated Mg-Doped GaN Layer

InGaN-GaN multiquantum-well (MQW) metal-semiconductor-metal (MSM) photodetectors (PDs) with the unactivated Mg-doped GaN cap layer were successfully fabricated. It was found that we could achieve a dark current by as much as six orders of magnitude smaller by inserting the unactivated Mg-doped GaN cap layer. For MSM photodetectors with the unactivated Mg-doped GaN cap layer, the responsivity at 380 nm was found to be 0.372 A/W when the device was biased at 5 V. The UV-to-visible rejection ratio was also estimated to be around 1.96 times 10³ for the photodetectors with the unactivated Mg-doped GaN cap layer. With a 5-V applied bias, we found that minimum noise equivalent power and normalized detectivity of our PDs were 4.09 times 10^-14 W and 1.18 times 10¹³ cmmiddotHz^0.5W^-1, respectively. Briefly, incorporating the unactivated Mg-doped GaN layer into the PDs beneficially brings about the suppression of dark current and a corresponding improvement in the device characteristics.     

InGaN/GaN MQW p–n junction photodetectors

InGaN/GaN multiquantum well (MQW) p–n junction photodetectors with semi-transparent Ni/Au electrodes were fabricated and characterized. It was found that the fabricated InGaN/GaN MQW p–n junction photodetectors exhibit a 20 V breakdown voltage and a 3.5 V forward 20 mA turn on voltage. It was also found that the photocurrent to dark current contrast ratio is higher than 10⁵ when a 0.4 V reverse bias was applied to the InGaN/GaN MQW p–n junction photodetectors. Furthermore, it was found that the maximum responsivity was 1.28 and 1.76 A/W with a 0.1 and 3 V applied reverse bias, respectively.     

GaN metal-semiconductor-metal photodetectors with low-temperature-GaN cap layers and ITO metal contacts

Nitride-based metal-semiconductor-metal (MSM) photodetectors (PDs) with low-temperature (LT) gallium nitride (GaN) cap layers and indium-tin-oxide (ITO) metal contacts were successfully fabricated. It was found that we could achieve three orders of magnitude smaller dark current by the introduction of the LT-GaN layer. For the PDs with LT-GaN cap layers, the maximum responsivity at 350 nm was found to be 0.1 and 0.9 A/W when the device was biased at 1 and 5 V, respectively. Operation speed of PDs with LT-GaN cap layers was also found to be faster than that of conventional PDs without LT-GaN cap layers.     

ZnSTeSe metal-semiconductor-metal photodetectors

High-quality quaternary ZnSTeSe epitaxial layers were successfully grown by molecular beam epitaxy (MBE). It was found that a ZnS_0.18 Se_0.82 layer was automatically formed in between the ZnSe buffer layer, and the ZnS_0.17Te_0.08Se_0.75 epitaxial layer, when we increased the ZnS cell temperature. ZnSTeSe metal-semiconductor-metal (MSM) photodetectors were also fabricated for the first time. It was found that we could achieve a photocurrent to dark current contrast higher than five orders of magnitude by applying a 10-V reverse bias. We also found that the maximum photoresponsivity is about 0.4 A/W under a 10-V reverse bias. Such a value suggests that the ZnSTeSe MSM photodetector is potentially useful in the blue-UV spectral region     

UV-Enhanced a-Si:H Metal–Semiconductor–Metal Photodetector

Planar metal–semiconductor–metal (MSM) photodetectors with very thin hydrogenated amorphous silicon (a-Si) films were fabricated for the detection of ultraviolet (UV) radiation. Since DNA and proteins strongly absorb UV radiation, these detectors find application in DNA and protein detection. The performance of top and bottom electrode MSM structures with aluminum electrodes is compared. The measured results include a responsivity of 150 mA/W and an external quantum efficiency of 74% at a wavelength of 260 nm for the top electrode configuration at a bias of 2 $hbox{V}/muhbox{m}$ and a 10- $muhbox{m}$ finger spacing.      

Performance of a near-infrared GaAs metal-semiconductor-metal (MSM)photodetector with islands

A GaAs metal-semiconductor-metal (MSM) photodetector with ultrasmall gold islands deposited on its photosensitive surface is described. The interdigitated detector is fabricated on a semi-insulating substrate in a MESFET-compatible technology. Responsivity as high as 1.8 A/W is obtained at 0.86 μm and a bias voltage of 8 V. This represents over a sixfold increase with respect to responsivity of a conventional MSM photodetector. The mechanism for dark current is suggested and breakdown characteristics are presented     

AlGaN MSM结构日盲型紫外探测器

采用低压-金属有机化学气相沉积(MOCVD)法在(0001)方向的AlN/蓝宝石模板上生长得到Al组分为40%的AlGaN材料,设计并制作了MSM型AlGaN日盲紫外探测器。通过HRXRD,SEM,AFM对AlGaN材料进行了表征,结果表明:该材料为六方相结构,且应变程度很小,粗糙度(RMS)为1.32 nm。通过测试器件在230³20 nm之间、在不同偏压下的光谱响应曲线,发现器件的截止波长在285 nm附近,截止边很陡峭;器件的峰值响应波长为275 nm;在7 V偏压下,器件峰值响应度达到最大2.8 mA/W;零偏压下,器件的暗电流1×10-13A,器件的暗电流很小。     

Novel NiGe MSM Photodetector Featuring Asymmetrical Schottky Barriers Using Sulfur Co-Implantation and Segregation

We report the first demonstration of a novel germanium (Ge) metal–semiconductor–metal (MSM) photodetector featuring asymmetrical Schottky-barrier height for low dark current and high-speed photodetection applications. Through co-implantation and segregation of valence-mending adsorbate such as sulfur at the NiGe/Ge interface, the germanide Fermi level can be pinned close to the conduction band edge. This results in an effective modulation of hole Schottky-barrier height, leading to a significant dark current suppression by $≫$3 orders of magnitude over a conventional MSM photodetector. When operated at a bias voltage $V_{A}$ of 1.0 V, a detector with an area of 804 $muhbox{m}^{2}$ shows a spectrum response of $sim$0.36 A/W or a corresponding quantum efficiency of $sim$34%. In addition, a frequency response measurement reveals the achievement of a $-$3-dB bandwidth of $sim!$15 GHz at an illumination photon wavelength of 1550 nm.      

Ultraviolet photodetector based on Au doped TiO2 nanowires array with low dark current

Au nanoparticles doped TiO2 nanowires (NWs) arrays with an average diameter of 100 nm were synthesized through a facile solvothermal method. Thereafter, metal/semiconductor/metal (MSM) structured detectors with Ag electrodes were fabricated on these NWs. The ultraviolet (UV) sensing characteristics of pure TiO2 and Au-doped ones (Au-TiO2) were investigated. Compared with pure TiO2, the Au-TiO2 NWs based device shows a much lower dark current of 1.5 nA at 3 V bias. The low dark current mechanism might be due to the promoted directional transmission of carriers induced by Au doping. The photoresponse is nearly one order of magnitude under 360 nm monochromatic illumination. The Au-TiO2 NWs detector with simple fabrication process, low noise and good overall performance provides a broad way in fabricating UV imaging arrays.     

Fabrication of ZnO nanowall-network ultraviolet photodetector on Si substrates

ZnO nanowall networks were prepared by plasma-assisted molecular beam epitaxy without a catalyst on Si(111) substrates.The nanostructures have preferred orientation along the c axis.The nanostructures are about 10 to 20 nm thick and about 50 nm tall.The planar geometry photoconductive type metal-semiconductor-metal photodetector based on the ZnO nanowall networks exhibits a high and wide response spectrum,and no decrease from 250 to 360 nm.With the applied bias below 5 V,the dark current was below 6μA,and the peak responsivity of 15 A/W was achieved at 360 nm.The UV(360 nm) to visible(450 nm) rejection ratio of around two orders could be extracted from the spectra response.     

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.     

4H-SiC金属-半导体-金属结构紫外探测器的模拟与分析

用MEDICI软件对金属-半导体-金属(MSM)结构4H-SiC紫外(UV)探测器的I-V特性以及光谱响应等特性进行了模拟与分析,并探讨了金属电极的宽度、电极间距以及外延层厚度对探测器响应度的影响.结果表明,室温下该探测器的暗电流线性密度达到10-13A/μm,且在不同电压下光电流至少比暗电流大两个数量级;探测器的光谱响应范围为200~400 nm,在347 nm处响应度达到极大值;增大指宽或者减小指间距可以提高探测器的响应度;当波长小于峰值波长时外延层厚度对探测器的响应度基本没影响,而当波长大于峰值波长时随着外延层厚度的增大探测器的响应度有所增大.     

N-doped ZnO based fast response ultraviolet photoconductive detector

We report a study on the fabrication and characterization of ultraviolet photodetectors based on N-doped ZnO films. Highly oriented N-doped ZnO films with 10 at.% N doping are deposited using spray pyrolysis technique onto glass substrates. The photoconductive UV detector based on N-doped ZnO thin films, having a metal–semiconductor–metal (MSM) configuration are fabricated by using Al as a contact metal. I–V characteristic under dark and UV illumination, spectral and transient response of ZnO and N-doped ZnO photodetector are studied. The photocurrent increases linearly with incident power density by more than two orders of magnitude. The photoresponsivity (580 A/W at 365 nm with 5 V bias, light power density 2 μW/cm²) is much higher in the ultraviolet region than in the visible.     

Nitride-based flip-chip p-i-n photodiodes

Nitride-based flip-chip p-i-n photodiodes were fabricated and characterized. It was found that we could achieve a small dark current of 5/spl times/10/sup -10/ A at -5 V and a large rejection ratio larger than three orders of magnitude. It was also found that the photodiodes only detect optical signals with wavelengths between 365 and 378 nm. Furthermore, it was found that peak responsivity occurs at around 370 nm with a value of 0.21 A/W at zero bias which corresponds to 70% external quantum efficiency.     

Reduction of dark current in AlGaN-GaN Schottky-barrier photodetectors with a low-temperature-grown GaN cap layer

AlGaN-GaN-based UV Schottky-barrier photodetectors with (i.e., sample A) and without (i.e., sample B) the low-temperature (LT) GaN cap layer were both fabricated. It was found that we could achieve a lower leakage current from sample A. Under reverse bias, it was found that sample A showed a dark current as low as 2/spl times/10/sup -11/ A at -5 V. In contrast, the dark current of sample B was at least one order of magnitude larger. With an incident light wavelength of 320 nm and a -1 V reverse bias, the measured responsivity was around 0.03 and 0.015 A/W for samples A and B, respectively.