| AVS 58th Annual International Symposium and Exhibition | |
| Thin Film Division | Thursday Sessions |
| Session TF1-ThM |
| Session: | Post-Deposition Processing and Characterization of Thin Films |
| Presenter: | Jonathan Lowder, Georgia Institute of Technology |
| Authors: | J.E. Lowder, Georgia Institute of Technology M.W. Moseley, Georgia Institute of Technology B. Gunning, Georgia Institute of Technology W.A. Doolittle, Georgia Institute of Technology M.E. Zvanut, University of Alabama J. Dashdorj, University of Alabama |
| Correspondent: | Click to Email |
Acceptor doping of III-Nitrides has been the subject of many studies due to the relativity low hole concentration (~1017-1018 cm-3) material commonly grown in contemporary devices. This limitation is thought to be one of the contributing factors to efficiency droop in LED’s. Recently, extremely high hole concentration (p>4x1019 cm-3) material with very high (>50%) ionization efficiency (see Fig. 1) has been demonstrated by metal modulated epitaxy (MME), an application of MBE where surface chemistry is controlled via shuttering of the source material [J. Appl. Phys. 106, 014905]. The samples in this study are characterized by temperature dependent Hall measurement to elucidate the reduction in the acceptor activation energy. Electron paramagnetic resonance spectroscopy (EPR) was used to show the microscopic view of the Mg acceptor without influence of the surrounding crystal as well as the effect of annealing temperature on the EPR signal. It is found that the primary transport mechanism is likely due to impurity band conduction, consistent with a distributed acceptor band as opposed to an isolated acceptor energy level as is generally observed in p-type GaN. Likewise, the interaction of the Mg with hydrogen shows different annealing behavior when compared to MOCVD p-type GaN.
The samples analyzed by EPR were annealed at various temperatures in forming gas (H2:N2). Fig. 2 shows the relative intensity from the EPR signal of the neutral Mg acceptor as a function of forming gas anneal temperature. It is clear that there is a sharp decrease in signal for the MME grown samples (doped >1020 Mg as seen in fig. 1) at 525 °C as compared to the drop observed at 750 °C for the MOCVD grown samples (doped ~1019 Mg). The exact nature of this temperature dependent decrease in signal is not fully understood, however it is suggested the different growth kinetics and resulting surface leads to a change in H2 transport. A second mechanism may be the formation of Mg-H complexes with varying activation energies.
Preliminary temperature dependent Hall results (Fig. 3) show an as-grown activation energy of 70 meV in the MME samples as well as 5x1018 cm-3 holes remaining at cryogenic temperatures. This extremely low activation energy and lack of carrier freeze out is evidence of impurity band conduction and shows the degenerative nature of the material. The full effect of the annealing temperature on this degenerative material will be presented in further detail as it pertains to device processing.