The Study On Ohmic Contact Based On GaN Under High-Temperature Environment And High-Current Density Stress Conditons

GaN, as the deputy of the third generation semiconductor, has excellent characteristics; Nowadays, it is one of the hottest issues. Ohmic contact is an important parameter to estimate the degeneration and. reliability of semiconductor device, for high-temperature LD and FET especially. It is necessary for ohmic contact to have low contact resistivity, good thermal stability. With the development of skill and technology, the reliability and lifetime of semiconductor device keep improving, a higher performance of devices is asked for, such as high temperature, low temperature, high-current density, radiation etc for the aerospace especially.We talked about the problems on theory and experiment from several aspects:Firstly, the research and development of measurement system: The system is divided into hardware and software. RS-3000 high-temperature oven is customized to meet the research requires of 500℃, and the high-temperature wire which nickel layer surrounds copper layer is customized too, which meets the requires for high-temperature and low resistance. To reach the measurement precision on line, each point measurement voltage is got by scan card, which assures all points to be measured at the same time. The software section is developed by Visual Basic, which can control high-temperature oven and KEITHLEY source equipments to measure, save data automatically.Secondly, study on high-temperature ohmic contact to n-GaN: many of different components and dope concentration samples, including Ti/Al/Ni/Au,Ti/Al/Pt/Au,Ti/Au/Pt/Au, dope concentration: 3.7×10¹⁷cm^-3, 3.0×10¹⁸cm^-3. The result shows that the contact resistivity of all samples increase with measurement temperature when the measurement temperature is upgraded 500℃, the thermal stability of heavily doped samples better than that of light ones. The contact resistivity increase with storage temperature and time, cannot recover the station before heating. The XRD and AES analysis shows that the Ni layer is not thick enough to cause the degeneration of ohmic contact before and after measuring.Thirdly, a kind of new method or structure is designed to measure the degeneration of ohmic contact under the high-current density. There are several ohmic contact electrons as the classic TLM method, and other corresponding several ohmic contact electrodes are connected each other by semiconductor films. The measurement method: firstly, the current is applied between A1 and B1, such as applied between A2 and B2…An and Bn. The ohmic contacts will produce failure to some extent with time and current density, but the semiconductor films are not destroyed among the electrodes in A section. That is to say, the TLM method is still employed to calculate contact resistivity but the B section for lacking the semiconductor films among the electrodes, which is subsidiary of A section.Fourthly, study on ohmic contact under high-current density. The samples are fabricated based on the new method, and solved a series of technology problems such as the wires disruption easily. The experiment results prove the coherent to design. The electromigration result in ohmic contact failure under the high-current density according to SEM and EDX.Finally, SPSS software is applied to estimate the distribution fitting based on the theory of reliability math model, and the failure rate is got according to parameter estimation.