In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.

Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

In this review article a comprehensive analysis of the developments in ultraviolet (UV) detector technology is described. At the beginning, the classification of UV detectors and general requirements imposed on these detectors are presented. Further considerations are restricted to modern semiconductor UV detectors, so the basic theory of photoconductive and photovoltaic detectors is presented in a uniform way convenient for various detector materials. Next, the current state of the art of different types of semiconductor UV detectors is presented. Hitherto, the semiconductor UV detectors have been mainly fabricated using Si. Industries such as the aerospace, automotive, petroleum, and others have continuously provided the impetus pushing the development of fringe technologies which are tolerant of increasingly high temperatures and hostile environments. As a result, the main efforts are currently directed to a new generation of UV detectors fabricated from wide band‐gap semiconductors the most promising ...

Semiconductor ultraviolet detectors

Silicon carbide (SiC), a material long known with potential for high-temperature, high-power, high-frequency, and radiation hardened applications, has emerged as the most mature of the wide-bandgap (2.0 eV ≲ Eg ≲ 7.0 eV) semiconductors since the release of commercial 6HSiC bulk substrates in 1991 and 4HSiC substrates in 1994. Following a brief introduction to SiC material properties, the status of SiC in terms of bulk crystal growth, unit device fabrication processes, device performance, circuits and sensors is discussed. Emphasis is placed upon demonstrated high-temperature applications, such as power transistors and rectifiers, turbine engine combustion monitoring, temperature sensors, analog and digital circuitry, flame detectors, and accelerometers. While individual device performances have been impressive (e.g. 4HSiC MESFETs with fmax of 42 GHz and over 2.8 W mm−1 power density; 4HSiC static induction transistors with 225 W power output at 600 MHz, 47% power added efficiency (PAE), and 200 V forward blocking voltage), material defects in SiC, in particular micropipe defects, remain the primary impediment to wide-spread application in commercial markets. Micropipe defect densities have been reduced from near the 1000 cm−2 order of magnitude in 1992 to 3.5 cm−2 at the research level in 1995.

Status of silicon carbide (SiC) as a wide-bandgap semiconductor for high-temperature applications: A review

Industries such as the automotive, aerospace or military, as well as environmental and biological research have promoted the development of ultraviolet (UV) photodetectors capable of operating at high temperatures and in hostile environments. UV-enhanced Si photodiodes are hence giving way to a new generation of UV detectors fabricated from wide-bandgap semiconductors, such as SiC, diamond, III-nitrides, ZnS, ZnO, or ZnSe. This paper provides a general review of latest progresses in wide-bandgap semiconductor photodetectors.

https://iopscience.iop.org/article/10.1088/0268-1242/18/4/201/pdf

Wide-bandgap semiconductor ultraviolet photodetectors

The energy distribution of electron states at SiC/SiO 2 interfaces produced by oxidation of various (3C, 4H, 6H) SiC polytypes is studied by electrical analysis techniques and internal photoemission spectroscopy. A similar distribution of interface traps over the SiC bandgap is observed for different polytypes indicating a common nature of interfacial defects. Carbon clusters at the SiC/SiO 2 interface and near-interfacial defects in the SiO 2 are proposed to be responsible for the dominant portion of interface traps, while contributions caused by dopant-related defects and dangling bonds at the SiC surface are not observed.

Intrinsic SiC/SiO2 Interface States

SiC photodiodes were fabricated using 6 H single-crystal wafers. These devices have excellent UV responsivity characteristics and very low dark current even at elevated temperatures. The reproducibility is excellent and the characteristics agree with theoretical calculations for different device designs. The advantages of these diodes are that they will operate at high temperatures and are responsive between 200 and 400 nm and not responsive to longer wavelengths because of the wide 3-eV bandgap. The responsivity at 270 nm is between 70% and 85%. Dark-current levels have been measured as a function of temperature that are orders of magnitude below those previously reported. Thus, these diodes can be expected to have excellent performance characteristics for detection of low light level UV even at elevated temperatures. >

Silicon carbide UV photodiodes

6H-SiC diodes fabricated using high-temperature nitrogen implantation up to 1000 degrees C are reported. Diodes were formed by RIE etching a 0.8- mu m-deep mesa across the N/sup +//P junction using NF/sub 3//O/sub 2/ with an aluminum transfer mask. The junction was passivated with a deposited SiO/sub 2/ layer 0.6 mu m thick. Contacts were made to N/sup +/ and P regions with thin nickel and aluminum layers, respectively, followed by a short anneal between 900 and 1000 degrees C. These diodes have reverse-bias leakage at 25 degrees C as low as 5*10/sup -11/ A/cm/sup 2/ at 10 V. >

Nitrogen-implanted SiC diodes using high-temperature implantation

It is well known that SiC can be thermally oxidized to form SiO/sub 2/ layers. And Si MOSFET IC's using thermally grown SiO/sub 2/ gate dielectrics are the predominant IC technology in the world today. However the SiC/SiO/sub 2/ interface has not been well characterized as was the case for Si MOS in the early 1960's. This paper presents data which for the first time characterizes the SiC/SiO/sub 2/ interface and explains one of the previously unexplained abnormalities observed in the characteristics of SiC MOSFET's. >

SiC MOS interface characteristics

Silicon carbide is one of the wide bandgap semiconductors that has been projected to have performances exceeding those of silicon and GaAs for high temperature and high-voltage power applications. Properties such as high electric breakdown field, high thermal conductivity, large saturated electron drift velocity, and excellent thermal stability make SiC a material of choice for high-power and high temperature operation. In SiC device fabrication, ion implantation of donor and acceptor impurities into SiC wafers is necessary to realize planar junctions, ohmic contacts, and numerous type of transistors. Although many efforts in improving the percentage of dopants activation and to decrease residual damages created during implantation process have been reported, the electrical behavior of the implanted SiC junctions has not been extensively studied. In this paper, we report a charge trapping phenomenon, unreported previously, in the n/sup +/p junctions of 6H-SiC formed by nitrogen implantation. This charge trapping causes excessive leakage current that decays slowly (/spl sim/msec) during reverse recovery.

Charge trapping in nitrogen implanted 6H-SiC n/sup +/p junctions

Latchup susceptibility over a temperature range of 25-315 degrees C for variations on a 1.2- mu m CMOS process is studied. A special high-performance process, including all refractory metallization, thinner epi, and higher doping levels, resulted in metal-migration immunity and doubling of the latchup holding voltage and current at 300 degrees C. >

E. Downey

Papers

Silicon carbide UV photodiodes

Nitrogen-implanted SiC diodes using high-temperature implantation

SiC MOS interface characteristics

Charge trapping in nitrogen implanted 6H-SiC n/sup +/p junctions

Junction-isolated CMOS for high-temperature microelectronics