Electro-Thermal-Mechanical Analysis of AlGaN/GaN Heterostructure Field Effect Transistor with SiO2/Si3N4 Passivation.

[[abstract]]The potential energy savings are huge: statistics from the US Department of Energy estimate that, by 2025, solid-state lighting such as LEDs could reduce the global amount of electricity used for lighting by 50% and, in the US alone, could eliminate 258 million metric tons of carbon emission, alleviate the need for 133 new power stations, and result in cumulative financial savings of over a hundred billion dollars.LEDs based on GaN, which emits brilliant light when electricity is passed through it, are extremely energy efficient and long lasting. In the UK, lighting consumes over a fifth of all the electricity generated at power stations, and GaN LEDs have the potential to reduce this figure by at least 50% and possibly by 75%.Gallium nitride is probably the most important semiconductor material since silicon. It can be used to emit brilliant light in the form of light emitting diodes (LEDs) and laser diodes, as well as being the key material for next generation high frequency, high power transistors capable of operating at high temperatures. Some of its prospects and applications are given a broader view below.? GaN for LDMOS Users: GaN HEMTs offer efficiency, bandwidth, and power advantages compared to Si LDMOS FETs. Making the switch to GaN involves assessing how the devices behave compared to Si LDMOS to understand what aspects of a design need to be rethought? Broadband Performance of GaN HEMTs: Broadband applications are the heart of today’s market for GaN RF power devices. The higher operating voltage and power density of GaN results in significant performance advantages for GaN in broadband applications.? Thermal Considerations for GaN Technology: GaN HEMTs offer much higher power density than competing technologies, providing significant performance advantages in many applications. However, this also leads to a thermal challenge of removing the heat from a relatively small FET area. The AlGaN/GaN HEMT devices possess a higher switching speed due to the high electron mobility and the high electron density of the 2DEG caused by polarization effect. But when the devices are used for high power and high current applications, the heating effect would be produced in the device channel. Recently, the GaN HEMT devices have been grown on Si substrates because it has some advantages about low cost, large area availability, and the acceptable thermal conductivity, the current dispersion effect in this epitaxy structure is therefore not obvious.The electrical reliability of RF power GaN high electron mobility transistors (HEMTs) has been recently improving. Still, these devices suffer from various degradation mechanisms that hamper their widespread deployment. Detailed physical understanding of the physics of failure in GaN HEMTs is essential before this technology can be widely adopted.Various phenomena related to the reliability of AlGaN/GaN HEMTs are investigated in this thesis using numerical simulations. We have carried out systematic experiments based on degradation mechanisms of GaN high electron mobility transistors (HEMT). The electro-thermo-mechanical properties of AlGaN/GaN are simulated for reliability testing under different temperature and bias conditions. The effect of surface passivation on undoped AlGaN/GaN HEMT is investigated using SiO2. We have also performed the electro-thermal simulations to study the effect of passivation on self heating, elastic energy and mechanical stress. Self heating phenomenon seems to be more uniform in case of passivated device. The SiO2 passivation layer reduces the elastic energy to about 20% comparison with unpassivated device under the gate edge. The elastic energy near the gate edge is reduced which is the critical region for defect formation.An alternative passivating layer which is Si3N4 is being used and compared with SiO2 passivation for electric field comparison with Schottky and Ohmic contacts. The effect stress on the electrical properties of the AlGaN/GaN has been discussed for SiO2 and Si3N4 deposition. Also effect of these films on the 2DEG density and I-V characteristics is investigated