| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Thursday Sessions |
| Session SS+AS+EM+EN-ThM |
| Session: | Semiconductor Surfaces and Interfaces - I |
| Presenter: | Joy McNamara, Virginia Commonwealth University |
| Authors: | J.D. McNamara, Virginia Commonwealth University K.L. Phumisithikul, Virginia Commonwealth University A.A. Baski, Virginia Commonwealth University M.A. Reshchikov, Virginia Commonwealth University J. Marini, SUNY Polytechnic Institute F. Shahedipour-Sandvik, SUNY Polytechnic Institute |
| Correspondent: | Click to Email |
AlGaN layers prepared by metal-organic chemical vapor deposition, with varying composition of Al (6 – 17%), were studied using the surface photovoltage (SPV) technique. Previous SPV studies on both n and p-type GaN allowed us to calculate the value of the surface band bending, by applying a thermionic model to explain the transfer of charges over the near surface barrier in various conditions (air, vacuum, and for a wide range of temperatures, T = 80 – 600 K). [1,2] The band bending was estimated to be 1.0 eV and – 2.0 eV, for n-type GaN and p-type GaN, respectively. SPV measurements on p-type AlGaN layers were expected to have similar behaviors to their p-type GaN counterparts. However, numerous measurements showed that this was not the case. The SPV transients (upon turning on or off the excitation source) showed significantly slower transients and smaller values than expected from the thermionic model. Moreover, the restoration of the band bending, as indicated by the restoration of the SPV signal to its dark value, did not occur within a reasonable amount of time. The data could not be fit by the thermionic model, and thus we were unable to calculate the band bending. We attribute the slow transients and lack of restoration to a defective surface region which interferes with thermionic processes. To verify this assumption, the top 40 nm of the AlGaN layer was etched using a reactive-ion etch (RIE). After etching, the SPV behavior exhibited substantially different behavior. Fast transients and close-to-thermionic behavior was recovered. Additionally, the effect of annealing the samples after etching provided even closer values to what is predicted by the thermionic model. From this study, it can be concluded that a defective, near surface region is inhibiting the transfer of holes over the near surface barrier under illumination, and hole trapping may be occurring during restoration. In both cases, this behavior cannot be modeled by theory. Etching removes the defective layer, and reveals a region of presumably higher quality as evidenced by the subsequent thermionic behavior.
[1] M. A. Reshchikov, M. Foussekis, and A. A. Baski. J. Appl. Phys. 107, 113535 (2010).
[2] M. Foussekis, J. D. McNamara, A. A. Baski, and M. A. Reshchikov, Appl. Phys. Let.101, 082104 (2012).