Zhang Yi-Men

Interfacial characteristics of Al/Al2O3/ZnO/n-GaAs MOS capacitor

The interfacial characteristics of Al/Al2O3/ZnO/n-GaAs metal—oxide—semiconductor (MOS) capacitor are investigated. The results measured by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) show that the presence of ZnO can effectively suppress the formations of oxides at the interface between the GaAs and gate dielectric and gain smooth interface. The ZnO-passivated GaAs MOS capacitor exhibits a very small hysteresis and frequency dispersion. Using the Terman method, the interface trap density is extracted from C–V curves. It is found that the ZnO layer can effectively improve the interface quality

Investigation of a 4H—SiC metal—insulation—semiconductor structure with an Al2O3/SiO2 stacked dielectric

Atomic layer deposited (ALD) Al2O3/dry-oxidized ultrathin SiO2 films as a high-k gate dielectric grown on 8° off-axis 4H—SiC (0001) epitaxial wafers are investigated in this paper. The metal—insulation—semiconductor (MIS) capacitors, respectively with different gate dielectric stacks (Al2O3/SiO2, Al2O3, and SiO2) are fabricated and compared with each other. The I—V measurements show that the Al2O3/SiO2 stack has a high breakdown field (≥12 MV/cm) comparable to SiO2, and a relatively low gate leakage current of 1 × 10−7 A/cm2 at an electric field of 4 MV/cm comparable to Al2O3. The 1-MHz high frequency C—V measurements exhibit that the Al2O3/SiO2 stack has a smaller positive flat-band voltage shift and hysteresis voltage, indicating a less effective charge and slow-trap density near the interface.

a DC-DC boost converter based on SiC MOSFET and SiC SBD

Power devices based upon silicon technology are rapidly approaching their theoretical limits of performance. Consequently, it will be necessary to develop devices from other materials in the future in order to reduce power losses in high frequency systems and in order to achieve high efficiencies. This paper presents a DC-DC boost converter based on SiC MOSFET and SiC Schottky Barrier Diode(SBD). This study focuses on demonstrating the capability of a DC/DC boost converter based on SiC devices in the applications at high switch frequency and high temperature operation. The simulation of the DC-DC boost converter is performed with the ISE-TCAD. The simulation results show that a switching frequency of 20 kHz, an output voltage of 500V and the output voltage ripples of 1%. In the steady state of the 20 kHz DC-DC boost converter simulation, the input power is 1248W, the output power is 1200W and the efficiency is as high as 96.1%.

Characteristics of blocking voltage for power 4H-SiC BJTs with mesa edge termination

According to the avalanche ionization theory, a computer-based analysis is performed to analyze the struc- tural parameters of single- and multiple-zone junction termination extension (JTE) structures for 4H-SiC bipolar junc- tion transistors (BJTs) with mesa structure. The calculation results show that a single-zone JTE can yield high breakdown voltages if the activated JTE dose and the implantation width are controlled precisely and a multiple-zone JTE method can decrease the peak surface field while still maintaining a high blocking capability. The influences of the positive and negative surface or interface states on the blocking capability are also shown. These conclusions have a realistic meaning in optimizing the design of a mesa power device.

High energy electron radiation effect on Ni/4H-SiC SBD and Ohmic contact

The Ni/4H-SiC Schottky barrier diodes (SBDs) and transfer length method (TLM) test patterns of Ni/4H-SiC Ohmic contacts were fabricated, and irradiated with 1 MeV electrons up to a dose of 3.43 × 1014 e/cm−2. After radiation, the forward currents of the SBDs at 2 V decreased by about 50%, and the reverse currents at −200 V increased by less than 30%. Schottky barrier height (oB) of the Ni/4H-SiC SBD increased from 1.20 eV to 1.21 eV under 0 V irradiation bias, and decreased from 1.25 eV to 1.19 eV under −30 V irradiation bias. The degradation of oB could be explained by the variation of interface states of Schottky contacts. The on-state resistance (Rs) and the reverse current increased with the dose, which can be ascribed to the radiation defects in bulk material. The specific contact resistance (ρc) of the Ni/SiC Ohmic contact increased from 5.11 × 10−5 Ω.cm2 to 2.97 × 10−4 Ω.cm2.

0.15-μm T-gate In0.52Al0.48As/In0.53Ga0.47As InP-based HEMT with fmax of 390 GHz

In this paper, 0.15-μm gate-length In0.52Al0.48As/In0.53Ga0.47As InP-based high electron mobility transistors (HEMTs) each with a gate-width of 2 × 50 μm are designed and fabricated. Their excellent DC and RF characterizations are demonstrated. Their full channel currents and extrinsic maximum transconductance (gm,max) values are measured to be 681 mA/mm and 952 mS/mm, respectively. The off-state gate-to-drain breakdown voltage (BVGD) defined at a gate current of −1 mA/mm is 2.85 V. Additionally, a current-gain cut-off frequency (fT) of 164 GHz and a maximum oscillation frequency (fmax) of 390 GHz are successfully obtained; moreover, the fmax of our device is one of the highest values in the reported 0.15-μm gate-length lattice-matched InP-based HEMTs operating in a millimeter wave frequency range. The high gm,max, BVGD, fmax, and channel current collectively make this device a good candidate for high frequency power applications.

Investigation of surface morphology and ion activation of aluminium implanted 4H-SiC

Multiple-energy aluminium (Al+) implantation into 4H-SiC (0001) epilayer and activation anneal with a graphite encapsulation layer were investigated in this paper. Measurements showed that the implanted Al+ box doping profile was formed and a high ion activation ratio of 78% was achieved by 40 min annealing at 1600°C using a horizontal chemical vapor deposition (CVD) reactor. The step bunching effect associated with the high temperature post implantation activation annealing (PIA) process was dramatically suppressed by using the graphite encapsulation layer. And a flat and smooth surface with a small average surface roughness (RMS) value of around 1.16 nm was achieved for the implanted 4H-SiC after the PIA process. It was demonstrated that this surface protection technique is a quite effective process for 4H-SiC power devices fabrication.

A broadband regenerative frequency divider in InGaP/GaAs HBT technology

A dynamic divide-by-two regenerative frequency divider (RFD) is presented in a 60-GHz-fT InGaP/GaAs heterojunction bipolar transistors (HBTs) technology. To achieve high operation bandwidth, active loads instead of resistor loads are incorporated into the RFD. On-wafer measurement shows that the divider is operating from 10 GHz up to at least 40 GHz, limited by the available input frequency. The maximum operation frequency of the divider is found to be much higher than fT/2 of the transistor, and also the divider has excellent input sensitivity. The divider consumes 300.85 mW from 5 V supply and occupies an area of 0.47 × 0.22 mm2.

Investigation of current transport parameters of Ti/4H-SiC MPS diode with inhomogeneous barrier

The current transport parameters of 4H-SiC merged PiN Schottky (MPS) diode are investigated in a temperature range of 300–520 K. Evaluation of the experimental current–voltage (I—V) data reveals the decrease in Schottky barrier height Φb but an increase in ideality factor n, with temperature decreasing, which suggests the presence of an inhomogeneous Schottky barrier. The current transport behaviours are analysed in detail using the Tungs model and the effective area of the low barrier patches is extracted. It is found that small low barrier patches, making only 4.3% of the total contact, may significantly influence the device electrical characteristics due to the fact that a barrier height of 0.968 eV is much lower than the average barrier height 1.39 eV. This shows that ion implantation in the Schottky contact region of MPS structure may result in a poor Ti/4H-SiC interface quality. In addition, the temperature dependence of the specific on-resistance (Ron—sp), T2.14, is determined between 300 K and 520 K, which is similar to that predicted by a reduction in electron mobility.

Neutron radiation effect on 4H-SiC MESFETs and SBDs

4H-SiC metal Schottky field effect transistors (MESFETs) and Schottky barrier diodes (SBDs) were irradiated at room temperature with 1 MeV neutrons. The highest neutron flux and gamma-ray total dose were 1 × 1015 n/cm2 and 3.3 Mrad(Si), respectively. After a neutron flux of 1 × 1013 n/cm2, the current characteristics of the MESFET had only slightly changed, and the Schottky contacts of the gate contacts and the Ni, Ti/4H-SiC SBDs showed no obvious degradation. To further increase the neutron flux, the drain current of the SiC MESFET decreased and the threshold voltage increased. B of the Schottky gate contact decreased when the neutron flux was more than or equal to 2.5 × 1014 n/cm2. SiC Schottky interface damage and radiation defects in the bulk material are mainly mechanisms for performance degradation of the experiment devices, and a high doping concentration of the active region will improve the neutron radiation tolerance.