This paper reviews the main aspects of the design, fabrication and characterization of GaAs Gunn diodes intended to be used in advanced driver assistance systems. The corresponding Gunn diode based oscillators operate at the microwave frequency of 77 GHz and deliver an output power up to 19.2 dBm (83.2 mW). To fulfill the high demands of the automotive industry, temperature stability and a high grade of frequency purity, the Gunn diode structure includes a hot electron injector. This is based on the heteroepitaxy of a graded gap AlxGa1-xAs layer and an adjacent thin highly doped GaAs layer. The hot electron injector properties are investigated using dc and rf electrical measurements, including the temperature influence as well. Specific production related data of the cavity oscillators using our Gunn diodes are presented. New alternatives, such as the resonant tunneling emitter as a hot electron injector and the Gunn diode based MMIC as oscillator, are introduced.

Hot electron injector Gunn diode for advanced driver assistance systems

We report on the high-voltage, noise, and radio frequency (RF) performances of aluminium gallium nitride/gallium nitride (AlGaN/GaN) on silicon carbide (SiC) devices without any GaN buffer. Such a GaN–SiC hybrid material was developed in order to improve thermal management and to reduce trapping effects. Fabricated Schottky barrier diodes (SBDs) demonstrated an ideality factor n at approximately 1.7 and breakdown voltages (fields) up to 780 V (approximately 0.8 MV/cm). Hall measurements revealed a thermally stable electron density at N2DEG = 1 × 1013 cm−2 of two-dimensional electron gas in the range of 77–300 K, with mobilities μ = 1.7 × 103 cm2/V∙s and μ = 1.0 × 104 cm2/V∙s at 300 K and 77 K, respectively. The maximum drain current and the transconductance were demonstrated to be as high as 0.5 A/mm and 150 mS/mm, respectively, for the transistors with gate length LG = 5 μm. Low-frequency noise measurements demonstrated an effective trap density below 1019 cm−3 eV−1. RF analysis revealed fT and fmax values up to 1.3 GHz and 6.7 GHz, respectively, demonstrating figures of merit fT × LG up to 6.7 GHz × µm. These data further confirm the high potential of a GaN–SiC hybrid material for the development of thin high electron mobility transistors (HEMTs) and SBDs with improved thermal stability for high-frequency and high-power applications.

AlGaN/GaN on SiC Devices without a GaN Buffer Layer: Electrical and Noise Characteristics.

The electronic transport in low-dimensional materials is controlled by quantum coherence and non-equilibrium statistics. The scope of the present investigation is to search for the origins of negative-differential resistance (NDR) behavior in N-doped ultra-narrow zigzag-edge ZnO nano-ribbons (ZnO-NRs). A state-of-the-art technique, based on a combination of density-functional theory (DFT) and non-equilibrium Green’s function (NEGF) formalism, is employed to probe the electronic and transport properties. The effect of location of N dopant, with respect to the NR edges, on IV-curve and NDR is tested and three different positions for N-atom are considered: (i) at the oxygen-rich edge; (ii) at the center; and (iii) at the Zn-rich edge. The results show that both resistance and top-to-valley current ratio (TVCR) reduce when N-atom is displaced from O-rich edge to center to Zn-rich edge, respectively. After an analysis based on the calculations of transmission coefficient versus bias, band structures, and charge-density plots of HOMO/LUMO states, one is able to draw a conclusion about the origins of NDR. The unpaired electron of N dopant is causing the curdling/localization of wave-function, which in turn causes strong back-scattering and suppression of conductive channels. These effects manifest themselves in the drawback of electric current (or so called NDR). The relevance of NDR for applications in nano-electronic devices (e.g., switches, rectifiers, amplifiers, gas sensing) is further discussed.

/pdf/origins-of-negative-differential-resistance-in-n-doped-zno-3zf0hkoe1m.pdf

Origins of Negative Differential Resistance in N-doped ZnO Nano-ribbons: Ab-initio Investigation

Gallium nitride (GaN)/porous silicon (PSi) film was prepared using a pulsed laser deposition method and 1064 nm Nd: YAG laser for optoelectronic applications and a series of Psi substrates were fabricated using a photoelectrochemical etching method assisted by laser at different etching times for 2.5–15 min at 2.5 min intervals. X-ray diffraction, room-temperature photoluminescence, atomic force microscopy and field emission scanning electron microscopy images, and electrical characteristics in the prepared GaN on the Psi film were investigated. The optimum Psi substrate was obtained under the following conditions: 10 min, 10 mA/cm2, and 24% hydrofluoric acid. The substrate exhibited two highly cubic crystalline structures at (200) and (400) orientations and yellow visible band photoluminescence, and homogeneous pores formed over the entire surface. The pores had steep oval shapes and were accompanied by small dark pores that appeared topographically and morphologically. The GaN/Psi film fabricated through PLD exhibited a high and hexagonal crystallographic texture in the (002) plane. Spectroscopic properties results revealed that the photoluminescence emission of the deposited nano-GaN films was in the ultraviolet band (374 nm) related to GaN material and in the near-infrared band (730 nm) related to the Psi substrate. The topographical and morphological results of the GaN films confirmed that the deposited film contained spherical grains with an average diameter of 51.8 nm and surface roughness of 4.8 nm. The GaN/Psi surface showed a cauliflower-like morphology, and the built-in voltage decreased from 3.4 to 2.7 eV after deposition. The fabricated GaN/Psi film exhibited good electrical characteristics. 

Effect of Different Etching Time on Fabrication of an Optoelectronic Device Based on GaN/Psi

Less contribution of nonradiative recombination in ZnO nails compared with rods

This research at Chungnam National University was supported by the Basic Research Program of the Korea Science & Engineering Foundation (Grant No. R01-2006-000-10874-0 / M10503000169-07M0300-16910) and partially supported by the Quantum Functional Semiconductor Research Center at Dongguk University.

Hydrogenation and Annealing Effects in n-Type ZnO Bulk Samples

Direct Current and Radio Frequency Characterizations of AlGaN/AlN/GaN/AlN Double‐Heterostructure High‐Electron Mobility Transistor (DH‐HEMT) on Sapphire

In this work, we have designed and fabricated the GaAs Gunn diodes for a 94 GHz waveguide voltage controlled oscillator (VCO) which is one of the important parts in a frequency modulated continuous wave (FMCW) radar application. For fabrication of the high power GaAs Gunn diodes, we adopted a graded gap injector which enhances the output power and conversion efficiency by effectively removing the dead-zone. We have measured RF characteristics of the fabricated GaAs Gunn diodes. The operating current, oscillation frequency, and output power of the fabricated GaAs Gunn diodes are presented as a function of the anode diameters. The operating current increases with anode diameters, whereas the oscillation frequency decreases. The higher oscillation frequency was obtained from 60 µm anode diameters of the fabricated Gunn GaAs diodes and higher power was obtained from 68 µm. Also, for application of the 94 GHz FMCW radar system, we have fabricated the 94 GHz waveguide VCO. From the fabricated GaAs Gunn diodes of anode diameter of 60 µm, we have obtained the improved VCO performance.

http://iopscience.iop.org/article/10.1143/JJAP.49.111202/pdf

Development of GaAs Gunn Diodes and Their Applications to Frequency Modulated Continuous Wave Radar

We investigate the effects of the number of gate fingers (N) and gate width (W) on the high-frequency characteristics of 0.1 µm depletion-mode metamorphic high-electron-mobility transistors (MHEMTs). The extracted gate-to-source capacitance (Cgs), gate-to-drain capacitance (Cgd), intrinsic transconductance (gm,int), and drain conductance (Gds) are proportional to total gate width (wt), whereas intrinsic resistance (Ri) and source resistance (Rs) are inversely proportional to wt. Gate resistance (Rg) linearly increases at various slopes with non-zero gate resistances at zero gate width depending on N. The cutoff frequency ( fT) and maximum frequency of oscillation ( fmax) are calculated using a small-signal model and curve-fitting equations extracted from each small-signal parameter. fT is almost constant; however, fmax is a strong function of Rg1/2 and is affected by both N and wt. A large wt produces a low fmax; however, at a given wt, increasing the number of gate fingers is more efficient than increasing single gate width for maximizing the fmax.

Radio Frequency Characteristics of Multifinger 0.1 µm Metamorphic High-Electron-Mobility Transistors Depending on Number of Gate Fingers and Gate Width

In this paper, we demonstrate the planar Schottky diode on GaAs substrate for terahertz applications A nanoscale dot and T-shaped disk has been developed as the anode for terahertz Schottky diode The low parasitic elements of the nanoscale anode with T-shaped disk yield high cutoff frequency characteristic The fabricated Schottky diode with anode diameter of 500 nm has series resistance of 21 Ω, ideality factor of 132, junction capacitance of 803 fF, and cutoff frequency of 944 GHz

http://koreascience.or.kr:80/article/JAKO201635551193552.pdf

Development of Planar Schottky Diode on GaAs Substrate for Terahertz Applications

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