| AVS 60th International Symposium and Exhibition | |
| Electronic Materials and Processing | Friday Sessions |
| Session EM+NS+SS+TF-FrM |
| Session: | Growth and Characterization of Group III-Nitride Materials |
| Presenter: | J. Hennessy, Jet Propulsion Laboratory, California Institute of Technology |
| Authors: | J. Hennessy, Jet Propulsion Laboratory, California Institute of Technology L.D. Bell, Jet Propulsion Laboratory, California Institute of Technology S. Nikzad, Jet Propulsion Laboratory, California Institute of Technology P. Suvarna, College of Nanoscale Science and Engineering, University at Albany F. Shahedipour-Sandvik, College of Nanoscale Science and Engineering, University at Albany |
| Correspondent: | Click to Email |
The detection of ultraviolet light has important applications in planetary imaging and spectroscopy, communications, and defense-related photosensing. One major challenge facing UV detection is visible-rejection, as UV photons in bands of interest are often greatly outnumbered by visible photons, effectively reducing the signal-to-noise ratio. Conventional systems for these detection applications include high-gain photomultiplier tubes and microchannel plate systems, which tend to be large, fragile, and require high-voltage operation. For these reasons, a more reliable all-solid-state alternative such as an avalanche photodiode (APD) is a desirable replacement option. III-N APDs based on the GaN/AlGaN material system are one candidate that can potentially offer high gain as well as visible-blind operation.
Significant materials challenges remain in order to improve the performance of AlGaN/GaN APDs, including the optimization of both bulk and surface defects. Sidewall-related defects in GaN APDs have often been observed to contribute to undesirable current components such as those produced by defect-related microplasmas. Although several approaches have been reported to address edge leakage issues, device repeatability and reliability remains a concern. In this work we investigate the effect of sidewall Al2O3 deposited by atomic layer deposition (ALD) as an alternative to more typical approaches like SiO2 deposited by plasma-enhanced chemical vapor deposition (PECVD). ALD is an attractive option for III-N sidewall passivation due to the ease in depositing potentially more compatible materials with the AlGaN system, as well the ability to conformally coat three dimensional structures like mesa diodes.
The use of ALD Al2O3 as a sidewall passivation layer was observed to result in the reduced occurrence of premature breakdown in mesa p-i-n GaN APDs when compared to devices fabricated with a more common SiO2 passivation deposited by PECVD. Mesa APDs with diameters ranging from 25 to 100 µm show a significant reduction in median dark current for the ALD-passivated devices. The reduction in median dark current was most significant for the smallest devices, showing an order of magnitude improvement at reverse biases near avalanche. The interfacial effect of ALD Al2O3 was investigated by fabricating MOS capacitors which show a large reduction in both slow trapping and faster interface states compared to PECVD SiO2 devices.