Point defect determination by photoluminescence and capacitance-voltage characterization in a GaN terahertz Gunn diode

Photoluminescence （PL） measurement is used to study the point defect distribution in a GaN terahertz Gunn diode, which is able to the degrade high-field transport characteristic during further device operation. PL, secondary ion mass spectroscopy （SIMS）, transmission electron microscope （TEM）, and capacitance-voltage （C-V） measurements are used to discuss the origin of point defects responsible for the yellow luminescence in structures. The point defect densities of about 1011 cm-2 in structures are extracted by analysis of C-V characterization. After thermal annealing treatment, diminishments of point defect densities in structures are efficiently demonstrated by PL and C-V results.

Design and manufacture of planar GaAs Gunn diode for millimeter wave application

GaAs-based planar Gunn diodes with A1GaAs hot electron injector have been successfully developed to be used as a local oscillator of 76 GHz in monolithic millimeter-wave integrated circuits. We designed two kinds of structure diode, one has a fixed distance between the anode and cathode, but has variational cathode area, the other has a fixed cathode area, but has different distances between two electrodes. The fabrication of Gunn diode is performed in accordance with the order of operations： cathode defining, mesa etching, anode defining, isolation, passivation, via hole and electroplating. A peak current density of 29.5 kA/cm^2 is obtained. And the charavteristics of negative differential resistance and the asymmetry of the current-voltage curve due to the A1GaAs hot electron injector are discussed in detail. It is demonstrated that the smaller size of active area corresponds to the smaller current, and the shorter distance between anode and cathode also corresponds to the lower threshold voltage and higher peak current, and hot electron injector can effectively enhance the radio frequency conversion efficiency and output power.

Notch-δ-doped InP Gunn diodes for low-THz band applications

The viability of the indium phosphide(InP)Gunn diode as a source for low-THz band applications is analyzed based on a notch-δ-doped structure using the Monte Carlo modeling.The presence of theδ-doped layer could enhance the current harmonic amplitude(A0)and the fundamental operating frequency(f0)of the InP Gunn diode beyond 300 GHz as compared with the conventional notch-doped structure for a 600-nm length device.With its superior electron transport properties,the notch-δ-doped InP Gunn diodes outperform the corresponding gallium arsenide(GaAs)diodes with up to 1.35 times higher in f0 and 2.4 times larger in A0 under DC biases.An optimized InP notch-δ-doped structure is estimated to be capable of generating 0.32-W radio-frequency(RF)power at 361 GHz.The Monte Carlo simulations predict a reduction of 44%in RF power,when the device temperature is increased from 300 K to 500 K;however,its operating frequency lies at 280 GHz which is within the low-THz band.This shows that the notch-δ-doped InP Gunn diode is a highly promising signal source for low-THz sensors,which are in a high demand in the autonomous vehicle industry.

The design and manufacture of a notch structure for a planar InP Gunn diode

A planar InP-based Gunn diode with a notch doping structure is designed and fabricated for integration into millimeter-wave and terahertz integrated circuits.We design two kinds of InP-based Gunn diodes.One has a fixed diameter of cathode area,but has variable spacing between anode and cathode;the other has fixed spacing,but a varying diameter.The threshold voltage and saturated current exhibit their strong dependences on the spacing（10 μm-20 μm） and diameter（40 μm-60 μm） of the InP Gunn diode.The threshold voltage is approximately 4.5 V and the saturated current is in a range of 293 mA-397 mA.In this work,the diameter of the diode and the space between anode and cathode are optimized.The devices are fabricated using a wet etching technique and show excellent performances.The results strongly suggest that low-cost and reliable InP planar Gunn diodes can be used as single chip terahertz sources.

Progress in Group Ⅲ nitride semiconductor electronic devices

Recently there has been a rapid domestic development in group iII nitride semiconductor electronic materials and devices. This paper reviews the important progress in GaN-based wide bandgap microelectronic materials and devices in the Key Program of the National Natural Science Foundation of China, which focuses on the research of the fundamental physical mechanisms of group III nitride semiconductor electronic materials and devices with the aim to enhance the crystal quality and electric performance of GaN-based electronic materials, develop new GaN heterostructures, and eventually achieve high performance GaN microwave power devices. Some remarkable progresses achieved in the program will be introduced, including those in GaN high electron mobility transistors （HEMTs） and metal-oxide-semiconductor high electron mobility transistors （MOSHEMTs） with novel high-k gate insulators, and material growth, defect analysis and material properties of InAlN/GaN heterostructures and HEMT fabrication, and quantum transport and spintronic properties of GaN-based heterostructures, and high- electric-field electron transport properties of GaN material and GaN Gunn devices used in terahertz sources.