A Hybrid Readout Solution for GaN-Based Detectors Using CMOS Technology.

Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100–300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness.

The Avalanche Photodiode (APD) is a unique device that combines the advantages of solid state photodetectors with those of high gain devices such as photomultiplier tubes (PMTs). APDs have internal gain that provides a high signal-to-noise ratio. APDs have high quantum efficiency, are fast, compact, and rugged. These properties make them suitable detectors for important applications such as LADAR, detection and identification toxic chemicals and bio-warfare agents, LIDAR fluorescence detection, stand-off laser induced breakdown spectroscopy (LIBS), and nuclear detectors and imagers. Recently there have been significant technical breakthroughs in fabricating very large APDs, APD arrays, and position sensitive APD arrays (PSAPD). Signal gain of over 10,000 has been achieved, single element APDs have been fabricated with active area greater than 40 cm², monolithic pixelated arrays with up to 28 x 28 elements have been fabricated, and position sensitive APDs have been developed and tested. Additionally, significant progress has been made in improving the fabrication process to provide better uniformity and high yield, permitting cost effective manufacturing of APDs for reduced cost.

Commercial flow cytometers use photomultiplier tubes (PMTs) for fluorescence detection. These detectors have high linear gain and broad dynamic range, but have limited sensitivity in the red and near infrared spectral regions. We present a comparison of avalanche photodiodes (APDs) and PMTs as detectors in flow cytometry instruments, and demonstrate improved sensitivity and resolution in the red and near infrared spectral regions using the APD. The relative performance of the PMT and APD were evaluated by simultaneously measuring the mean fluorescence intensity and coefficient of variation for emission from light emitting diode pulses, flow cytometry test beads, and fluorescently labeled cells. The relative signal to noise performance of the APD and PMT was evaluated over the 500 nm to 1050 nm wavelength range using pulsed light emitting diode light sources. While APDs have higher quantum efficiency but lower internal gain than PMTs, with appropriate external amplification the APD has signal to noise response that is comparable to PMTs in the 500 nm to 650 nm range and improved response in the 650 nm to 850 nm range The data demonstrates that the APD had performance comparable to the PMT in the spectral region between 500 to 650 nm and improved performance in the range of 650 to 1000 nm, where the PMT performance is quite poor. CD4 positive lymphocyte populations were easily identified in normal human blood both by APD and PMT using phycoerythrin labeled antibodies. In contrast, only the APD detector could resolve CD4 positive populations using 800 nm Quantum dot labeled antibodies.

Icy worlds of the outer solar system contain tantalizing evidence of habitability and potential life. These bodies also present extra exploration challenges due to the harsh environmental conditions at the surfaces. Thus, robust and reliable detectors are necessary for the in situ spectroscopic identification of astrobiologically relevant compounds deposited on the icy surface, entrained in thick atmospheres, or rafted in plumes. In addition, the distinction between prebiotic, extant, and relict organic molecules in such environments is needed to address life detection goals. The Ultra-Violet Detector Innovation for Raman Exploration and CharacTerization (UV-DIRECT) of ocean worlds project focuses on the development SiC- avalanche photodiode (APD) technology for UV-Raman spectroscopy and Raman imaging. Si-based Single Photon Avalanche Diodes (SPADs) have been developed for time resolved Raman spectroscopy in recent years, but SiC (Silicon Carbide) APD detectors have advantages over them. Our detector is an ultra-compact, radiation and temperature tolerant, visible blind device that has high quantum efficiency (QE) in the DUV (~260 nm) but poorer performance in the near ultraviolet (NUV) between 300-340nm that is important for Raman Spectroscopy. Our approach to improve this combines a series of numerical models with laboratory testing to enhance the QE response and ultimately the single photon detection efficiency in the NUV (~340 nm). Raman spectroscopy has established itself in current missions as an information-rich, non-contact, non-destructive method for identifying and characterizing inorganic and organic compounds in a wide variety of planetary materials. UV/NUV-Raman spectroscopy is well-suited to characterizing plume materials and surface ice deposits, since it especially sensitive to organic compounds and inorganic salts improved sensitivity due to the combination of resonance effects and the lack of background fluorescence and less risk of sample damage compared to excitation with wavelengths

Integration of low voltage analog and logic circuits as well as high-voltage (HV) devices for operation at greater than 5 V enables Smart Power ICs used in almost any system that contains electronics. HVCMOS (High-Voltage CMOS) technologies offer much lower process cost, if compared to BCD technologies, they enable multiple HV levels on a single chip, and need less effort when scaling to smaller CMOS technology nodes or when integrating embedded non-volatile memory. In this work we propose a new 0.35 µm HVCMOS technology that can overcome the previous limitations in drive currents. It can match the low HV chip sizes (Rdson) of typical BCD processes while maintaining the low process complexity with only 2 mask level adders on top of CMOS. We also introduce a figure of merit (FOM) for comparing HV technologies. Key elements of making this newly proposed 0.35 µm HVCMOS so competitive to BCD technologies are discussed and a device lifetime of more than 10 years, operating temperatures of 150 °C and ESD robustness of 4 kV HBM and higher, as well as the integration of a highly robust embedded EEPROM/Flash technology is shown. We also provide first verification results of the scalability of the proposed 0.35 µm HVCMOS technology to 0.18 µm and beyond as well as to currents of up to 8 A.

This paper carries out a series of the analysis of the power system using gallium nitride (GaN) FET which has a wide band gap (WBG) characteristics comparing to the conventional silicon (Si) MOSFET-used power system. At first, for the comparison of each semiconductor device, the switching-transient parameter is quantitatively extracted from the released information of GaN FET. And GaN FET model which reflect this dynamic property is configured. By using this model, the performance of GaN FET is analyzed comparing to Si MOSFET. As a result, GaN FET power system, designed by the optimal point suggested in this paper, can reduce the loss by 25.5% and the volume by 78.6% of major components comparing conventional Si MOSFET power system.

The Laboratoire Electronique et Traitement de l’Information (LETI) of the Commissariat a l’Energie Atomique (CEA, Grenoble, France) has been involved in the development of infrared detectors based on HgCdTe (MCT) material for over 30 years, mainly for defence and security programs [1]. Once the building blocks are developed at LETI (MCT material process, diode technology, hybridization, …), the industrialization is performed at SOFRADIR (also in Grenoble, France) which also has its own R&D program [2]. In past years, LETI also developed infrared detectors for space astrophysics in the mid infrared range – the long wave detector of the ISOCAM camera onboard ISO – as well as in the far infrared range – the bolometer arrays of the Herschel/PACS photometer unit –, both instruments which were under the responsibility of the Astrophysics department of CEA (IRFU/SAp, Saclay, France). Nowadays, the infrared detectors used in space and ground based astronomical instruments all come from vendors in the US. For programmatic reasons – increase the number of available vendors, decrease the cost, mitigate possible export regulations, …– as well as political ones – spend european money in Europe –, the European Space Agency (ESA) defined two roadmaps (one in the NIR-SWIR range, one in the MWIR-LWIR range) that will eventually allow for the procurement of infrared detectors for space astrophysics within Europe. The French Space Agency (CNES) also started the same sort of roadmaps, as part of its contribution to the different space missions which involve delivery of instruments by French laboratories. It is important to note that some of the developments foreseen in these roadmaps also apply to Earth Observations. One of the main goal of the ESA and CNES roadmaps is to reduce the level of dark current in MCT devices at all wavelengths. The objective is to use the detectors at the highest temperature where the noise induced by the dark current stays compatible with the photon noise, as the detector operating temperature has a very strong impact at system level. A consequence of reaching low levels of dark current is the need for very low noise readout circuits. CEA and SOFRADIR are involved in a number of activities that have already started in this framework. CEA/LETI does the development of the photo-voltaic (PV) layers – MCT material growth, diode technologies–, as well as some electro-optical characterisation at wafer, diode and hybrid component levels, and CEA/IRFU/SAp does all the electro-optical characterisation involving very low flux measurements (mostly dark current measurements). Depending of the program, SOFRADIR can also participate in the development of the hybrid components, for instance the very low noise readout circuits (ROIC) can be developed either at SOFRADIR or at CEA/LETI. Depending of the component specifications, the MCT epitaxy can be either liquid phase (LPE, which is the standard at SOFRADIR for production purposes) or molecular beam (MBE), the diode technology can be n/p (standard at LETI and SOFRADIR) or p/n (under development for several years now) [3], and the input stage of the ROIC can be Source Follower per Detector (SFD for very low flux low noise programs) or Capacitive Trans Impedance Amplifier (CTIA for intermediate flux programs) [4]. This paper will present the different developments and results obtained so far in the two NIR-SWIR and MWIR-LWIR spectral ranges, as well as the perspectives for the near future. CEA/LETI is also involved in the development of MCT Avalanche Photo Diodes (APD) that will be discussed in other papers [5,6].

HgCdTe has been shown to be the first semiconductor exhibiting single-carrier multiplication in avalanche photodiodes (APDs) up to gain values larger than 1000 and with close to zero excess noise. These results have opened a new windows for low-flux and versatile imaging. In this paper, we report the latest results on MWIR HgCdTe APDs manufactured at SITP. These APDs display a gain of 1000 around 10V reverse bias. The excess noise factor is between 1.2 to 1.45 up to gain of 100, and the quantum efficiency is more than 60% from 1μm wavelength to peak wavelength 4.2 μm. These results show that the technological processes used at SITP are well adapted to APD manufacturing. However, at present, the dark current starts increasing significantly faster than the gain at high bias, and then the device becomes dark current noise limited. APD gain performance was successfully modeled by the simulation of electrical characteristics used Synopsys Sentaurus based on Okuto-Crowell ionizaition coefficient model. Therefore, Sentaurus would be used as a powerful predictive tool for SITP technology and stress its reproducibility and optimize the devices .

At high reverse bias, semiconductor diodes break down by the avalanche effect. This can be used to advantage, for example, in avalanche photodiodes in which avalanche multiplication can improve the signal‐to‐noise ratio. This article reviews the fundamental physics of avalanche multiplication, including its effects on signal‐to‐noise ratio and frequency response.

Gallium nitride (GaN) has great potential applications in the field of high-frequency and high-power electronic devices because of its excellent material properties such as wide band gap, high electron mobility, high breakdown field strength. However, the high power GaN electronic device also exhibits significant self-heating effects in operation, such as a large amount of Joule heat localized in the thermal channel, and heat dissipation has become a bottleneck in its applications. The interface thermal conductance (ITC) between GaN and its substrate is the key to determining the thermal dissipation. In this work the various GaN interface defects and their effects on ITC are first discussed, and then some methods of studying interface thermal transport are introduced, including theoretical analysis and experimental measurements. Then, some GaN ITC optimization strategies developed in recent years are introduced through comparing the specific cases. In addition to the common chemical bond interface, the weak coupling interface by van der Waals bond is also discussed. Finally, a summary for this review is presented. We hope that this review can provide valuable reference for actually designing GaN devices.

We report on the development and application of a flow cytometer using a 16-channel avalanche photodiode (APD) linear detector array. The array is configured with a dispersive grating to simultaneously record emission over a broad wavelength range using the 16 APD channels of the linear APD array. The APD detector elements have a peak quantum efficiency of 80% near 900 nm and have at least 40% quantum efficiency over the 400-nm to 1000-nm wavelength range. The extended red sensitivity of the detector array facilitates the use of lower energy excitation sources and near IR emitting dyes which reduces the impact of autofluorescence in signal starved measurements. The wide wavelength sensitivity of the APD array permits the use of multiple excitation sources and many different fluorescent labels to maximize the number of independent parameters in a given experiment. We show the sensitivity and linearity measurements for a single APD detector. Initial results for the flow cytometer with the 16-element APD array and the 16-channel readout ASIC (application specific integrated circuit) are presented.

The higher critical electric field of β-gallium oxide (Ga2O3) gives promise to the development of next generation power electronic devices with improved size, weight, power, and efficiency over current state-of-the-art wide bandgap devices based on 4H-silicon carbide (SiC) and gallium nitride (GaN). However, it is expected that Ga2O3 devices will encounter serious thermal issues due to the poor thermal conductivity of the material. In this work, self-heating in Ga2O3 Schottky barrier diodes under different regimes of the diode operation was investigated using diverse optical thermography techniques including thermoreflectance thermal imaging, micro-Raman thermography, and infrared thermal microscopy. 3D coupled electro-thermal modeling was used to validate experimental results and to understand the mechanism of heat generation for the diode structures. Measured top-side and cross-sectional temperature fields suggest that device and circuit engineers should account for the concentrated heat generation that occurs near the anode/Ga2O3 interface and/or the lightly doped drift layer under both forward and high voltage reverse bias conditions. Results of this study suggest that electro-thermal co-design techniques and top-side thermal management solutions are necessary to exploit the full potential of the Ga2O3 material system.

Influence of shallow versus deep etching on dark current and quantum efficiency in InAs/GaSb superlattice photodetectors and focal plane arrays for long wavelength infrared detection

Chapter 5 - Gan-Based Modulation-Doped Field-Effect Transistors and Ultraviolet Detectors

Wide band-gap (WBG) semiconductors technology represents a potential candidate to displace conventional silicon (Si) technology used in power electronics. Between Silicon Carbide (SiC) and Gallium Nitride (GaN) power semiconductors, the latter is the least mature of both technologies, with many open research problems, especially in the aerospace industry. In this paper, we address the design and implementation of a DC/DC converter for a hybrid small unmanned aerial vehicle (UAV) based on GaN technology. Both theoretical and simulation comparisons of Si, SiC and GaN transistors for the converter are presented. The conclusion is that GaN devices are the most appropriate to fulfill converter requirements for the size and weight limitations of the selected UAV. The paper presents a buck converter which handles an input voltage range of 32 V to 40 V and provides a 12 V regulated output and output power up to 60 W. The experimental results carried out on the prototype converter show how promising the GaN technology is for aerospace systems, not only regarding its volume and size, but also its efficiency. Besides, practical implementation details are reported to contribute to the design of small, light and reliable GaN power converters for aeronautics.