A Strategic Review of Reduction of Dislocation Density at the Heterogenious Junction of GAN Epilayer on Foreign Substrate

Now-a-days for long range microwave communication, especially for space applications, devices capable to operate at a high power and high frequency are desired. Compound Semiconductor (CS), mainly Gallium Nitride (GaN) based heterostructure electronic devices are the only available solutions till now to fulfil these criteria. However, looking from a cost and manufacturing perspective, GaN substrate has considerable drawbacks like non-availability, expense as well as compulsion to use older technologies for device designing as the wafer diameter is small. A potential solution for performance/cost dilemma is to grow high quality GaN as active layer on a well matured substrate by metamorphic technique. Metamorphic buffer technology allows the device designer an additional degree of freedom to optimize the transistor at high frequency for high gain and power applications. But this metamorphic buffer technology has some drawbacks, too. The main limiting factor for this technology is the propensity to develop dislocation at the heterojunction due to lattice mismatch between the grown layer and the substrate. A good quality metamorphic buffer can only be achieved by reduction of dislocation density at the heterojunction. This paper reviews the progress being made towards reduction of dislocation density of GaN based devices grown on Silicon Carbide (SiC), Sapphire (Al₂O₃) and Si substrate, respectively, in terms of material parameters and growth issues.