GaN-on-Diamond Felix Ejeckam November 14, 2006

24. We would like to make sure that the GaN will stay attached to the diamond during temperature excursions because Otherwise the material would not be terribly useful. We would like to make sure that the GaN will stay attached to the diamond during temperature excursions because Otherwise the material would not be terribly useful.

26. In this study, samples of GaN-on-diamond are compared to GaN-on-silicon, as grown. We are not introducing additional strains. No shift in the PL peak at high temperature. The shift at low temperature can have to do with the differences in expansion coefficients. Can see that the wiggles indicate a higher quality material. All samples show roughly same BE energy, S1 and S2 also show similar defect luminescence. Energy difference negligible now At room temperature, free excitons do not exist, only excitons bound to impurities. In this study, samples of GaN-on-diamond are compared to GaN-on-silicon, as grown. We are not introducing additional strains. No shift in the PL peak at high temperature. The shift at low temperature can have to do with the differences in expansion coefficients. Can see that the wiggles indicate a higher quality material. All samples show roughly same BE energy, S1 and S2 also show similar defect luminescence. Energy difference negligible now At room temperature, free excitons do not exist, only excitons bound to impurities.

27. Band edge region (LT: 18K): Back of the envelope calculation shows thermal expansion mismatch for GaN/Si vs. GaN/diamond accounts for ~5 meV energy difference (18K-295K). Conclusion: the approx. 35meV shift at LT between Ref. and S1/S2 is not dominantly described by thermal expansion differences (lift off?). Band edge region (LT: 18K): Back of the envelope calculation shows thermal expansion mismatch for GaN/Si vs. GaN/diamond accounts for ~5 meV energy difference (18K-295K). Conclusion: the approx. 35meV shift at LT between Ref. and S1/S2 is not dominantly described by thermal expansion differences (lift off?).

28. Known defect bands. Can be caused by many different defects. The Ref sample seems to have good XTAL quality, based on the fact that we can resolve the separate BE (band edge peaks). I’ve labeled them as BX (bound exciton) and FX (free exciton). The S1 and S2 samples do not show this resolution. (The shoulder at lower energies than BX in the Ref sample, however, is still unknown, could be due to a shallow donor level.) Known defect bands. Can be caused by many different defects. The Ref sample seems to have good XTAL quality, based on the fact that we can resolve the separate BE (band edge peaks). I’ve labeled them as BX (bound exciton) and FX (free exciton). The S1 and S2 samples do not show this resolution. (The shoulder at lower energies than BX in the Ref sample, however, is still unknown, could be due to a shallow donor level.)

29. Blue luminescence might have contributions from extended defects, but not the yellow. May make a difference for optics. Most likely not for electronics. Blue is not metastable (nitrogen vacancy) Yellow luminescence are point defects, and do not charge. Don’t expect the point defects to be very problematic. Not active at room temperature. If the material had become conductive it would not show this temperature dependence. Does not have an immediate effect on the conductance.Blue luminescence might have contributions from extended defects, but not the yellow. May make a difference for optics. Most likely not for electronics. Blue is not metastable (nitrogen vacancy) Yellow luminescence are point defects, and do not charge. Don’t expect the point defects to be very problematic. Not active at room temperature. If the material had become conductive it would not show this temperature dependence. Does not have an immediate effect on the conductance.

30. Variations can come from the original materials. Our changes, if any are smaller than the variations in original material. Symmetric rocking curve is always better because you are looking straight in on the sample.Variations can come from the original materials. Our changes, if any are smaller than the variations in original material. Symmetric rocking curve is always better because you are looking straight in on the sample.

31. Cause for double peak. Rocking curve, sitting at a specific spot and moving the detector along, which gives you a variation of the crystaline quality. Normal coupled scan you are moving the beam as well as the angle, so you may move over a defect… In the normal coupled scan you can get the lattice constant.Cause for double peak. Rocking curve, sitting at a specific spot and moving the detector along, which gives you a variation of the crystaline quality. Normal coupled scan you are moving the beam as well as the angle, so you may move over a defect… In the normal coupled scan you can get the lattice constant.

32. GaN species composition is unchanged by diamond process (PL MAP) GaN crystal quality mostly unchanged by diamond process (X-ray) Low Temperature PL results are affirmative GaN crystal is substantially less strained than GaN-on-Si or GaN-on-SiC Slight increase in defect luminescence – may be from in-plane 2D interfacial defects. SEM do not show any vertical migration up the GaN crystal 2D electron gas Unchanged by diamond process!