Electrical and ultraviolet characterization of 4H-SiC Schottky photodiodes

Fabrication and electrical and optical characterization of 4H-SiC Schottky UV photodetectors with nickel silicide interdigitated contacts is reported. Dark capacitance and current measurements as a function of applied voltage over the temperature range 20 °C – 120 °C are presented. The results show consistent performance among devices. Their leakage current density, at the highest investigated temperature (120 °C), is in the range of nA/cm2 at high internal electric field. Properties such as barrier height and ideality factor are also computed as a function of temperature. The responsivities of the diodes as functions of applied voltage were measured using a UV spectrophotometer in the wavelength range 200 nm - 380 nm and compared with theoretically calculated values. The devices had a mean peak responsivity of 0.093 A/W at 270 nm and −15 V reverse bias

High-responsivity SiC Ultraviolet Photodetectors with SiO2 and Al2O3 Films

Silicon carbide (SiC) has shown considerable potential for ultraviolet (UV) photodetectors due to its properties such as wide band gap (3.26 eV for 4H-SiC), high break down electric field and high thermal stability. 4H-SiC-based UV photodetectors such as Schottky, metal-semiconductor-metal (MSM), metal-insulator-semiconductor (MIS) and avalanche have been presenting excellent performance for UV detection application in flame detection, ozone-hole sensing, short-range communication, etc. Generally, the most widely used antireflection coating and passivation layer for 4H-SiC-based photodetectors are native SiO2 grown by heating 4H-SiC in O2 in order to improve the absorption and passivation of photodetectors. Nevertheless, the thermally grown SiO2 single layer suffers from high reflection, large absorption and inaccurate thickness. Therefore, in this chapter, UV antireflection coatings were designed, fabricated and applied in order to reduce optical losses and improve the quantum efficiency (QE) of 4H-SiC-based photodetectors. The important results will be introduced as follows

Ultraviolet photon-counting single-pixel imaging

We demonstrate photon-counting single-pixel imaging in the ultraviolet region. Toward this target, we develop a high-performance compact single-photon detector based on a 4H-SiC single-photon avalanche diode (SPAD), where a tailored readout circuit with active hold-off time is designed to restrain detector noise and operate the SPAD in free-running mode. We use structured illumination to reconstruct 192$\times$192 compressed images at a 4 fps frame rate. To show the superior capability of ultraviolet characteristics, we use our single-pixel imaging system to identify and distinguish different transparent objects under low-intensity irradiation, and image ultraviolet light sources. The results provide a practical solution for general ultraviolet imaging applications.Comment: 5 pages, 5 figures, accepted for publication in Applied Physics Letter

Simulation and Fabrication of 4H-SiC Separated Absorption Charge and Multiplication Ultraviolet Avalanche Photodiodes

4H-碳化硅（SiC）紫外雪崩光电探测器（APD）已具备取代紫外光电倍增管和Si基紫外光电探测器的可能性，它在光纤通信、高保密的非视距紫外通信及微弱紫外信号检测等特殊领域有重要的应用，已日益成为国际上光电探测领域的研究热点。 近年来已报道的高性能4H-SiCAPDs大多是采用吸收层和倍增层分离结构（SAM）进行制备。虽然SAM结构具有较高的量子效率，但是为了实现有效的吸收层和倍增层分离结构，要求倍增层厚度较薄且掺杂浓度较高，这将会使得器件的暗电流较大且倍增层电场分布梯度过大，不利于雪崩机制，并导致器件雪崩击穿电压过大。为了解决这些问题，本论文改进传统4H-SiCSAM（p+nn-n+）结构，...High performance 4H-SiC ultraviolet (UV) avalanche photodiodes (APDs), as a potential candidate to replace UV photomultiplier tubes and Si-based UV photodiodes, play an important role in the fields such as optical fiber communication, non-line-of-sight covert communications and low-level UV detection, which have increasingly become an research hotspot in the photoelectric detection field. Recentl...学位：理学博士院系专业：物理科学与技术学院_凝聚态物理学号：1982008015050

Miniaturized Silicon Photodetectors

Silicon (Si) technologies provide an excellent platform for the design of microsystems where photonic and microelectronic functionalities are monolithically integrated on the same substrate. In recent years, a variety of passive and active Si photonic devices have been developed, and among them, photodetectors have attracted particular interest from the scientific community. Si photodiodes are typically designed to operate at visible wavelengths, but, unfortunately, their employment in the infrared (IR) range is limited due to the neglectable Si absorption over 1100 nm, even though the use of germanium (Ge) grown on Si has historically allowed operations to be extended up to 1550 nm. In recent years, significant progress has been achieved both by improving the performance of Si-based photodetectors in the visible range and by extending their operation to infrared wavelengths. Near-infrared (NIR) SiGe photodetectors have been demonstrated to have a “zero change” CMOS process flow, while the investigation of new effects and structures has shown that an all-Si approach could be a viable option to construct devices comparable with Ge technology. In addition, the capability to integrate new emerging 2D and 3D materials with Si, together with the capability of manufacturing devices at the nanometric scale, has led to the development of new device families with unexpected performance. Accordingly, this Special Issue of Micromachines seeks to showcase research papers, short communications, and review articles that show the most recent advances in the field of silicon photodetectors and their respective applications

Design, fabrication and characterization of III-nitride PN junction devices

Design, fabrication and characterization of III-Nitride pn junction devices Jae Boum Limb 94 pages Directed by Dr. Russell D. Dupuis This dissertation describes an investigation of three types of III-nitride (AlInGaN) based p-n junction devices that were grown by metalorganic chemical vapor deposition (MOCVD). The three types of devices are Ultra-Violet (UV) avalanche photodiodes (APDs), green light emitting diodes (LEDs), and p-i-n rectifiers. For avalanche photodiodes, a material growth on low-dislocation density GaN substrates, processed with low-damage etching receipes and high quality dielectric passivations, were proposed. Using this technology, GaN APDs with optical gains greater than 3000, and AlGaN APDs showing true avalanche gains have been demonstrated. For green LEDs, the use of InGaN:Mg as the p-layer, rather than employing the conventional GaN:Mg has been proposed. Green LEDs with p-InGaN have shown higher emission intensities and lower diode series resistances compared to LEDs with p-GaN. Using p-InGaN layers, LEDs emitting at green and longer wavelengths have been realized. For p-i-n rectifiers, design, fabrication and characterization of device structures using the conventional mesa-etch configuration, as well as the full-vertical method have been proposed. High breakdown devices with low on-resistances have been achieved. Specific details on device structures, fabrication methods, and characterization results are discussed.Ph.D.Committee Chair: Russell Dupuis; Committee Member: David Citrin; Committee Member: Joy Laskar; Committee Member: Srinivas Garimella; Committee Member: William Doolittl

Electrooptical Characterization of New Classes of Silicon Carbide UV Photodetectors

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HIGH PERFORMANCE III-NITRIDE ULTRAVIOLET AVALANCHE PHOTODETECTORS

In this dissertation, two projects are demonstrated: 1) Al0.6Ga0.4N p-i-n avalanche photodiode (APD) and 2) the low-temperature Geiger-mode measurement system for a GaN p-i-n APD. In the first project, the AlGaN APD structure is designed, grown by metalorganic chemical vapor deposition on an aluminum nitride (AlN) bulk substrate and on two different crystalline quality AlN/sapphire templates. The AlGaN APD structure is then fabricated into circular devices with a diameter of 20 um starting with 1) reactive-ion etching (RIE) of mesa structure 2) n-type and p-type metal stacks patterning with electron-beam evaporation, 3) passivation of the surface with plasma enhanced chemical vapor deposition (PECVD) silicon oxide and RIE etching for via holes, and 4) metal pads deposition for wire-bonding. The APD devices showed the reverse breakdown voltage around -140V, which corresponds to a breakdown electric field of 6~6.2MV/cm for the Al0.6Ga0.4N material as estimated by TCAD Silvaco simulation. The APD devices grown on the AlN bulk substrate exhibited the lowest leakage current density below 1 × 10଼/ଶ compared to that of the devices grown on the AlN templates. The maximum photocurrent gain of 1.2 × 10ସ at 250nm of light was calculated. The average temperature coefficients of the breakdown voltage are negative for the APD devices but these data show that the coefficient is the largest with the devices grown on the low-dislocation-density AlN bulk substrate. in the second project, the low-temperature Geiger-mode measurement system was constructed by integrating a device driver circuit system, an ultraviolet (UV) illumination system, and a low-temperature control system. The principle of single-photon detection is studied based on the Poisson statistics. In the low temperature control system, a thermoelectric cooler module was used to control the temperature of the device in the range of -40 to 20°C. With the constructed Geiger-mode measurement system, the temperature dependence of the breakdown voltage of the GaN APD was measured 0.0159 ± 0.0034 V/K. Dark count rate (DCR) as a function of different temperature set points was exhibited and discovered that the dominant mechanism contributing to the DCR of the GaN APD is band-to-band tunneling. Finally, the photon detection efficiency (PDE) of the APD as a function of excess bias at different temperature set points was exhibited and found that the PDE is independent of the temperature set points.Ph.D