| AVS 64th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Tuesday Sessions |
| Session EM+SS-TuA |
| Session: | Surface and Interface Challenges in Semiconductor Materials and Devices |
| Presenter: | Chien-Fong Lo, IQE |
| Authors: | C.F. Lo, IQE O. Laboutin, IQE X. Gao, IQE C.K. Kao, IQE H. Marchand, IQE W. Johnson, IQE R. Pelzel, IQE |
| Correspondent: | Click to Email |
Gallium nitride based devices have been delivering their promise of high power and high frequency operation as a capable replacement for silicon based devices, applications, owing to highly desirable III-nitride physical properties [1] . However, device performance is limited by excessive Schottky gate leakage, which results in high gate subthreshold leakage and leakage instability. These in turn cause high off-state drain leakage, a degradation of power efficiency, and ultimately device reliability problems.
Schottky leakage is caused by an excessive trap states density at the interface between the Schottky gate and the nitride semiconductor, resulting in excess negative charges on the barrier surface and/or in the barrier layer that induce current collapse in off-state operation. Dielectric capping of the III-nitride structure is one method to suppress the gate leakage in both forward and reverse bias, thereby mitigating current collapse and further improving the 3-terminal breakdown. Passivation with silicon nitride has been reported to reduce the current collapse and provide a relatively low state density at the SiNx/III-N interface [2] and is widely used. However, in many instances, the SiNx passivation is done ex-situ from the GaN epi system which results in an oxide layer at the nitride/SiNx interface, which in turn reduces the efficacy of the passivation. Therefore, it is desirable to perform the SiNx deposition in-situ so that the semiconductor/SiNx interface is oxide-free.
In-situ, MOCVD SiNx films have been grown on 100–200 mm Si substrates and characterized with RBS, AFM, XRD/XRR, and C-V profiling. Stoichiometric silicon nitride films with good surface morphology and material properties have been achieved. Metal-insulator-semiconductor HEMT (MISHEMT) devices with in-situ SiNx capping layer were fabricated and compared with conventional GaN-capped HEMTs. Devices with in-situ passivation exhibit three orders of magnitude lower gate leakage current and improved 3-terminal breakdown (200V improvement at 10 µA/mm, see Fig. 1). Hall–Van der Pauw measurements performed on both GaN- and SiNx-capped samples indicate that using in-situ SiNx results in a significant increase in channel carrier density, which is consistent with SiNx providing a reduced trap state density at the Schottky/semiconductor interface [3]. Additional electrical data including pulsed I-V will be presented to validate the improvements in switching performance. All of the nitride-based materials and SiNx passivation layers have been grown using a commercial MOCVD reactor ensuring cost-effective implementation for commercial power-switching applications.