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The Study on Ohmic Contact Based on GaN under High-Temperature Environment and High-Current Density Stress Conditons

Author: ZhangYueZong
Tutor: FengShiWei
School: Beijing University of Technology
Course: Microelectronics and Solid State Electronics
Keywords: Ohmic contact Contact resistivity A high current density High-temperature properties High Temperature Storage
CLC: TN304
Type: PhD thesis
Year: 2009
Downloads: 224
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Abstract


GaN semiconductor material with its wide band gap, high electron saturation velocity advantages in high-temperature, high-power microwave devices become an important material for people research attention. Work GaN devices, device parameters as potential extreme environment degradation and reliability in harsh environments, the current research focus. The ohmic contact is a measure degradation of the semiconductor device and the reliability of the basic parameters, is also one of the problems must be solved in the device, especially for the FET device or a light emitting device under the high temperature environment and the large current density, contact resistivity , thermal stability, good ohmic contact to the device must have. Depth study of the GaN Ji Oumu contact the degradation characteristics of high-temperature environment (gt; 300 ℃), and high current density. In experimental and theoretical aspects, mainly the following aspects of the research work: an ohmic contact with the high temperature environment test system structures and development. This test system is divided into two parts, hardware and software. For the hardware part: RS-3000 high temperature box furnace designed Based meet the requirements of high temperature (500 ℃), designed to meet the high-temperature low-resistance high temperature nickel-copper-clad wire requirements; quick scan to test accuracy, scan card is the measured voltage, to ensure that the measured point data collected at the same temperature. For the software part of the application VB independent development of visual programming, high temperature furnace, KEITHLEY current source control, and automated measurement sample, the data is automatically saved. , GaN Ji Oumu exposure to elevated temperature properties. Preparation of a variety of different alloy systems, samples of different doping concentrations, mainly including: Ti / Al / Ni / Au, Ti / Al / Pt / Au, Ti / Au / Pt / Au, the doping concentration is divided into: 3.7 × 1017cm -3, 3.0 × 1018cm-3 two. And the test temperature was elevated to 500 ° C, the results show that: all the contact resistance of the sample rate is increased as the ambient temperature rises; heavily doped samples better thermal stability than the lightly doped samples; the contact resistance of the all samples rate with increasing storage temperature increased with storage time; contact resistivity unrecoverable degradation characteristics; indicates that the X-ray spectroscopy and Auger electron spectroscopy test analysis before and after sample storage, ohmic contact degradation due to Ni The blocking layer is not thick enough to each other so that the contact layer and the cap layer of metal infiltration and seepage, thereby destroying the good ohmic contact. Three, designed a new method and structure of the rate of degradation of the ohmic contact resistance at high current density test, and declare the invention patent. This test method is based on the traditional TLM method, access to the subsidiary electrode B in the conventional contact next to the electrodes A, A portion of traditional transmission line structure, B part each between adjacent electrodes are the insulating underlayer, A, B part of the contact electrode The inter-connected by a semiconductor material. First of A, B is applied between the examination current (within a certain time plus a certain current density), and then disconnect the A, B between examination current measurement, only the part A total resistance and spacing between adjacent electrodes, application of transmission line method plotted and calculated the rate of contact resistance after the degradation of the part A of the ohmic contact. The structure and measuring method of the present invention is used, to avoid damage of the assessment of current on the semiconductor material, to accurately assess the degree of degradation of the ohmic contact. Expand the range of applications and fields of traditional TLM method. Fourth, a large current density in ohmic contact with the sample prepared by the process. To do a scientific analysis of the sample preparation possible problems and propose solutions to solve key technological problems successfully prepared based large current density experiment samples. Scanning electron microscopy analysis of the sample topography, chemical composition in the form of analysis of the energy spectrum of the sample before and after the test, the results show that the metal ion diffusion occurred in the large current density is the main cause sample failure. , Based on the mathematical theory of reliability model by SPSS (Statistical Package for the Social Sciences) mapping method to determine the fit test distribution parameter estimation related parameters measure calculated activation energy and get life; final failure of the sample is calculated rate.

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