Study Of The High Energy Particle Radiation Effect On 4H-SiC SBDs And MESFETs

Silicon Carbide (SiC) has outstanding properties such as wide bandgap, higher thermal conductivity, high breakdown field and high radiation tolerance, and it has been used to fabricate the devices operated in high temperature, high power, and high radiation hardness. There is a great interest in the radiation effect on SiC device because of the potential applications in the space, nuclear power industry and military area.Among various types of SiC electronic devices, the SiC Schottky barrier diodes (SBDs) and Metal Semiconductor Field Effect Transistors (MESFETs) become mature and show the attractive application potential. There are several problems in the research of radiation effects on SiC SBDs and MESFETs: (1) The damage mechanisms caused by high energe particle are not sufficiently revealed by experiment evidence; (2) The previously reported radiation study of SiC SBDs were generally performed at zero bias during irradiation, but in practical application, the SiC Schottky contacts often work in the reversed bias, for example in MESFET; (3) The study of radiation effects on SiC ohmic contacts has not been found in literatures; (4) The study of neutron radiation effect on SiC MESFET has been hardly found in the past.In this dissertation, the Ni, Ti/4H-SiC SBDs and MESFETs irradiated with gamma rays, high energy electrons and neutrons have been investigated. The radiation effects are obverved and the damage mechanisms are analyzed.And the SiC SBDs act as ionization radiation detectors and betavoltaic cells have been studied. The main studies and contributions of this dissertation are as follows:(1) Based on unintentionally doped n type 4H-SiC homoepitaxial layer of the free carrier concentration about 6.4×1014cm-3 obtained using a low pressure, hot wall CVD reactor. Ni, Ti/4H-SiC SBDs and TLM (Transfer Length Method) test patterns of Ni/4H-SiC ohmic contacts were fabricated. I-V and C-V characteristics of the SBDs demonstrated a well electrically performance. The decvice parameters like the schottky barrier height (φB), ideality factor and series resistance have been extracted by thermionic emission theory.(2) The Ni, Ti/4H-SiC SBDs were irradiated with the 60Co gamma ray source to the accumulated dose of 1Mrad(Si). The 0V and -30V bias voltage were applied to the SBDs during irradiation. The on-line current and the annealing effect in room temperature were monitored to analyze the damage mechanism. After 1Mrad(Si) radiation,φ_B and ideality factor of the Ni, Ti/4H-SiC SBDs under different bias voltage basicly remain the same values, and minority carrier lifetime of the epitaxial layer also has no degradation. The reverse current decreases after radiation, which can be explained by the negative surface charge increase. The results show radiation bias voltage has no influence on the Ni, Ti/4H-SiC SBDs.(3) The Ni, Ti/4H-SiC SBDs and TLM test patterns were irradiated with 1MeV electrons up to a dose of 3.43×10¹⁴e/cm². The 0V and -30V bias voltage were applied to the SBDs during irradiation. After radiation,φ_B of the Ni and Ti/4H-SiC SBDs showed opposite degradation trend. Under different radiation bias voltage,φ_B of the Ti/4H-SiC SBDs showed similar degradation trend, but different degradation trend for Ni/4H-SiC SBDs. After one week annealing in room temperature,φ_Bof the Ni and Ti/4H-SiC SBDs under different radiation bias voltages had completely recovered to the value before radiation. The reverse currents of the Ni/4H-SiC SBDs slightly increased, but for Ti/4H-SiC SBDs it basically remained the same values. The on-state resistances of all diodes increased with the dose, which can be ascribed to the radiation defects. The radiation degradation of the Ni/SiC ohmic contacts is also observed.(4) The 4H-SiC SBDs and MESFETs were irradiated at room temperature with 1MeV neutrons. The highest neutron flux and gamma total dose was 1×10^/(15)n/cm² and 3.3Mrad(Si). Increasing with the neutron flux, the drain current of MESFET decreased and the threshold voltage increased. However no obviously degration forφ_B of the gate Schottky contacts of the Ni and Ti/4H-SiC SBDs has been observed at the neutron flux of 1×10¹³n/cm², but decreased at flux of 2.5×10¹⁴n/cm².(5) A numerical model is proposed based on the investigation of the operational mechanism for ionization radiation detector of the reverse biased 4H-SiC schottky diode. The detector characteristics of dark current, current response and sensitivity at different bias voltages and irradiation doses are simulated. The results from simulation agree with the experimental data very well. And the Ni and Ti/4H-SiC SBDs act as ionization radiation detector to be measured.(6) The Ni/4H-SiC SBD betavoltaic cell was measured under irradiation from 63Ni source. The MCNP is used to calculate the energy loss of the beta particles pass through the Schottky electrode metal. An underestimated power conversion efficiency of 2.81% is obtained. The result shows the potential of the SiC SBD acted as betavoltaic cell.