A field effect transistor, a bipolar transistor, a PIN diode, a Schottky rectifier or other high voltage semiconductor device comprise a semiconductor body having a depletion layer formed throughout a portion in at least a high voltage mode of operation of the device, such as, by reverse biasing a rectifying junction. The known use of a single high-resistivity body portion of one conductivity type to carry both the high voltage and to conduct current results in a series resistivity increasing approximately in proportion with the square of the breakdown voltage. This square-law relationship is avoided by the present invention in which a depleted body portion comprising an interleaved structure of first and second regions of alternating conductivity types carries the high voltage which occurs across the depleted body portion. The thickness and doping concentration of each of these first and second regions are such that when depleted the space charge per unit area formed in each of these regions is balanced at least to the extent that an electric field resulting from any imbalance is less than the critical field strength at which avalanche breakdown would occur in the body portion. The first regions in at least one mode of operation of the device provide electrically parallel current paths extending through the body portion.

High voltage semiconductor device

Silicon nitride films were deposited at low temperatures (245–370 °C) and high deposition rates (500–1700 A/min) by hot filament assisted chemical vapor deposition (HFCVD). Optical properties of these amorphous silicon nitride thin films have been extensively characterized by absorption, photoluminescence (PL), photoluminescence excitation, and electroluminescence measurements. The optical band gap of the films was varied between 2.43 and 4.74 eV by adjusting the flow rate of the disilane source gas. Three broad peaks at 1.8, 2.4, and 3.0 eV were observed in the PL spectra from these films. A simple qualitative model based on nitrogen and silicon dangling bonds adequately explains the observed PL features. The photoluminescence intensity observed in these films was 8–10 times stronger than films deposited by plasma enhanced chemical vapor deposition, under similar conditions. The high deposition rates obtained by HFCVD is believed to introduce a large number of these optically active defects.

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Optical properties of silicon nitride films deposited by hot filament chemical vapor deposition

Superjunction has arguably been the most creative and important concept in the power device field since the introduction of the insulated gate bipolar transistor (IGBT) in the 1980s. It is the only concept known today that has challenged and ultimately proved wrong the well-known theoretical study on the limit of silicon in high-voltage devices. This paper deals with the history, device and process development, and the future prospects of Superjunction technologies. It covers fundamental physics, technological challenges as well as aspects of design and modeling of unipolar devices, such as CoolMOS. The superjunction concept is compared to other methods of enhancing the conductivity of power devices (from bipolar to employment of wide-bandgap materials) to derive its set of benefits and limitations. This paper closes with the application of the superjunction concept to other structures or materials, such as terminations, superjunction IGBTs, or silicon carbide Field Effect Transistors (FETs).

Superjunction Power Devices, History, Development, and Future Prospects

A family of novel three-terminal devices which relies on the transfer of a quasi-monoenergetic hot electron beam through a thin base is described. The devices are similar in principle to the proposed tunneling amplifier by Mead in the early sixties (“Cold Cathode” or “Metal Base” amplifiers). Results are reviewed and the probable reasons for the poor performances are pointed out. It is predicted that, with a proper choice of parameters, metal-base amplifiers can operate as switches, negative resistance devices and continuous amplifiers in the subpicosecond range. Two subclasses are described: The tunneling emitter (THETA), in the major part of the work, and the nontunneling emitter (BHETA) amplifiers. In the THETA family the metal-oxide-metal-oxide-metal (MOMOM), the MOM-semiconductor (MOMS), and the heterojunctions devices are described. Members of the BHETA family generate quasi-monoenergetic electron beams by injecting electrons by an n + n − or a metal- n − junctions, and include a variety of metals and semiconductor combinations. Very thin films are required in these devices (oxides ∼15 A, metals ∼100 A, semiconductors ∼100 A). The molecular beam epitaxy technique and lattice matching considerations are required for pinhole free semiconductors and metal films with minimum interface states. Sputter-oxidation methods are needed for thin oxide growth. Systems which combine these features with availability of microfabrication make these devices feasible today.

Tunneling hot electron transfer amplifiers (theta): Amplifiers operating up to the infrared

We disclose a high voltage semiconductor device comprising a semiconductor substrate of a second conductivity type; a semiconductor drift region of the second conductivity type disposed over the semiconductor substrate, the semiconductor substrate region having higher doping concentration than the drift region; a semiconductor region of a first conductivity type, opposite to the second conductivity type, formed on the surface of the device and within the semiconductor drift region, the semiconductor region having higher doping concentration than the drift region; and a lateral extension of the first conductivity type extending laterally from the semiconductor region into the drift region, the lateral extension being spaced from a surface of the device.

High voltage semiconductor devices

Single crystalline 3C‐SiC films were grown on a Si substrate by molecular beam epitaxy (MBE) using SiHCl3 and C2H4 gases. The optimal growth conditions were achieved at a growth temperature (Tsub ) of 1000 °C and a gas pressure ratio (PSiHCl3 /PC2H4 ) of 1/3 at PSiHCl3 =1×10−5 Torr. Prior to the essential growth of SiC, a carbonization process was performed with C2H4 gas only. A continuous observation by reflection high‐energy electron diffraction (RHEED) was performed throughout the process of crystal growth. A series of RHEED patterns revealed that carbonization film could be grown at 750 °C and the lattice mismatch between Si and SiC crystals was satisfactorily relaxed. All processes of crystal growth were performed at a relatively low temperature.

Low-temperature growth of 3C-SiC by the gas source molecular beam epitaxial method

Using the carbonization process, single‐crystalline SiC films were grown at substrate temperature (Tsub) in the range of 750–1050 °C by the gas‐source molecular‐beam epitaxial method. This process was performed by using C2H4 gas and a special growth method in which the temperature was raised at a predetermined rate (RT) during growth. To realize the growth of single‐crystalline carbonized films, it was found that a C2H4 gas pressure PC2H4=8×10−5 Torr and rising rate RT=25–25/3 °C/min were necessary. After the carbonization process, essential growth of SiC films using SiHCl3 and C2H4 gases in the range of gas pressure ratios PSiHCl3/PC2H4= (1)/(3) –5 (PSiHCl3=1–5×10−5 Torr) at Tsub=1000 °C was performed. In these all experimental ranges, single‐crystalline 3C‐SiC films could be grown.

Carbonization process for low‐temperature growth of 3C‐SiC by the gas‐source molecular‐beam epitaxial method

The chemical vapor deposition method using hydrogen radicals excited by microwave plasma has been applied to obtain silicon nitride (SiN) films of low hydrogen content. In this method, silane and monomethylamine were used as source gases. Various properties of deposited films such as the composition of SiN, the residual contents of carbon and oxygen, and the deposition rate were influenced by growth conditions. In the growth conditions, the distance between the center of the waveguide and the substrate was the most critical parameter because the distribution of the H radical strongly depended upon it in our experiment. For a suitable substrate position, carbon and oxygen contents could be reduced to a small value. On the other hand, residual hydrogen content was less than ~1×1022 cm-3. This value was a quarter of that in the films grown by silane and ammonia gases under similar conditions.

https://iopscience.iop.org/article/10.1143/JJAP.29.918/pdf

Chemical Vapor Deposition of Low Hydrogen Content Silicon Nitride Films Using Microwave-Excited Hydrogen Radicals

A study of a new type varactor diode which consists of a semiconductor multilayer structure has been performed. It is shown that such a varactor diode has much stronger nonlinearity in capacitance variation with applied bias voltage than does the conventional varactor due to the two‐dimensional expansion of the depletion region. First, the internal behaviors of this diode are investigated in detail by two‐dimensional computer simulation. Based on the physical insight obtained by the simulation, an approximate analytical expression for the voltage dependence of capacitance is derived for the purpose of practical design. Then, the proposed structure has been experimentally made from Si, whose capacitance‐voltage characteristics are compared with those of the conventional structure made from the same material. Those results substantiate the theoretical predictions.

New type of varactor diode consisting of multilayer p‐n junctions

Hot‐filament chemical vapor deposition (hot‐filament CVD) of silicon nitride films has been studied using silane and monomethylamine as source gases for the deposition temperature 600–800 °C. The deposition rate was about one order larger than that of thermochemical vapor deposition (thermo‐CVD) using the same gases. The activation energy of the growth rate was 0.2 eV smaller than that of thermo‐CVD. The hydrogen content was below the detection limit of infrared absorption measurements even in the film deposited at 600 °C. The film surface deposited at 700 °C had a smooth specular surface and the flatness of the hot‐filament CVD films was the same as that of thermo‐CVD films deposited at 100–200 °C higher temperatures.

Shigeo Kaneda

Papers

Low-temperature growth of 3C-SiC by the gas source molecular beam epitaxial method

Carbonization process for low‐temperature growth of 3C‐SiC by the gas‐source molecular‐beam epitaxial method

Chemical Vapor Deposition of Low Hydrogen Content Silicon Nitride Films Using Microwave-Excited Hydrogen Radicals

New type of varactor diode consisting of multilayer p‐n junctions

Amorphous SiN films grown by hot‐filament chemical vapor deposition using monomethylamine