Yonglai Tian

Microwave annealing of Mg-implanted and in situ Be-doped GaN

An ultrafast microwave annealing method, different from conventional thermal annealing, is used to activate Mg-implants in GaN layer. The x-ray diffraction measurements indicated complete disappearance of the defect sublattice peak, introduced by the implantation process for single-energy Mg-implantation, when the annealing was performed at ≥1400 °C for 15 s. An increase in the intensity of Mg-acceptor related luminescence peak (at 3.26 eV) in the photoluminescence spectra confirms the Mg-acceptor activation in single-energy Mg-implanted GaN. In case of multiple-energy implantation, the implant generated defects persisted even after 1500 °C/15 s annealing, resulting in no net Mg-acceptor activation of the Mg-implant. The Mg-implant is relatively thermally stable and the sample surface roughness is 6 nm after 1500 °C/15 s annealing, using a 600 nm thick AlN cap. In situ Be-doped GaN films, after 1300 °C/5 s annealing have shown Be out-diffusion into the AlN layer and also in-diffusion toward the GaN/SiC in...

Ultrahigh-temperature microwave annealing of Al+- and P+-implanted 4H-SiC

The GMU work is supported by Army Research Of- fice Dr. Prater under Grant No. W911NF-04-1-0428 and a subcontract from LT Technologies under NSF SBIR Grant No. 0539321.

Microwave Annealing of Very High Dose Aluminum-Implanted 4H-SiC

A microwave heating technique has been used for the electrical activation of Al+ ions implanted in semi-insulating 4H-SiC. Annealing temperatures in the range of 2000–2100 °C and annealing time of 30 s have been used. The implanted Al concentration has been varied from 5×1019 to 8×1020 cm-3. A minimum resistivity of 2×10-2 Ωcm and about 70% electrical activation of the implanted Al have been measured at room temperature for an implanted Al concentration of 8×1020 cm-3 and microwave annealing at 2100 °C for 30 s.

Characteristics of in situ Mg-doped GaN epilayers subjected to ultra-high-temperature microwave annealing using protective caps

Different protective caps (AlN, MgO, graphite) are investigated for their feasibility for protecting GaN surfaces during ultra-high-temperature (>1300 °C) microwave annealing. Compared to other capping materials, pulsed-laser-deposited AlN is found to protect the GaN surface more effectively, during ultra-fast microwave annealing at temperatures as high as 1500 °C. The RMS surface roughness (0.6 nm) of the GaN sample annealed at 1500 °C with an AlN cap in place is similar to the value (0.3 nm) measured on the as-grown sample. The photoluminescence and electrical measurements have indicated a decrease in the compensating deep donor concentration for the increasing microwave annealing temperature, as long as the surface integrity of the GaN epilayer is preserved. These results indicate the attractiveness of the AlN cap for microwave annealing of ion-implanted GaN.

Microwave Annealing of High Dose Al+-implanted 4H-SiC: Towards Device Fabrication

High-purity semi-insulating 8° off-axis 〈0001〉 4H-SiC was implanted with Al+ at different doses and energies to obtain a dopant concentration in the range of 5 × 1019–5 × 1020 cm−3. A custom-made microwave heating system was employed for post-implantation annealing at 2,000 °C for 30 s. Sheet resistance and Hall-effect measurements were performed in the temperature range of 150–700 K. At room temperature, for the highest Al concentration, a minimum resistivity of 3 × 10−2 Ω cm was obtained, whereas for the lowest Al concentration, the measured resistivity value was 4 × 10−1 Ω cm. The onset of impurity band conduction was observed at around room temperature for the samples implanted with Al concentrations ≥3 × 1020 cm−3. Vertical p+-i-n diodes whose anodes were made by 1.5 × 1020 cm−3 Al+ implantation and 2,000 °C/30 s microwave annealing showed exponential forward current–voltage characteristics with two different ideality factors under low current injection. A crossover point of the temperature coefficient of the diode resistance, from negative to positive values, was observed when the forward current entered the ohmic regime.

High dose Al + implanted and microwave annealed 4H-SiC

A post implantation microwave annealing technique has been applied for the electrical activation of Al+ implanted ions in semi-insulating 4H-SiC. The annealing temperatures have been 2000-2100°C. The implanted Al concentration has varied from 5 x 1019 to 8 x 1020 cm-3. A minimum resistivity of 2 x 10-2 Ω∙cm and about 70% electrical activation of the implanted Al has been measured at room temperature for an implanted Al concentration of 8 x 1020 cm-3 and a microwave annealing at 2100°C for 30 s.

Microwave Annealing of Ion Implanted 4H‐SiC

Ultra‐fast high‐temperature microwave annealing at temperatures as high as 2050 °C for 30 s has been performed on phosphorus ion‐implanted 4H‐SiC for phosphorus doping concentrations in the range 5×1019 cm−3–8×1020 cm−3. For comparison, inductive heating furnace anneals were performed at 1800 °C–1950 °C for 5 min. Electrical resistivity of the P+‐implanted samples decreased with increasing annealing temperature reaching a minimum value of 6.8×10−4 Ωcm for 2050 °C/30 s microwave annealing and a slightly higher value for 1950 °C/5 min inductive heating furnace annealing. X‐ray rocking curve measurements showed that the microwave annealing not only removed the lattice damage introduced by the ion‐implantation process, but also the defects present in the original virgin sample as well.

Microwave annealing of ion implanted 6H-SiC

Microwave rapid thermal annealing has been utilized to remove the lattice damage caused by nitrogen (N) ion-implantation as well as to activate the dopant in 6H-SiC. Samples were annealed at temperatures as high as 1,400 C, for 10 min. Van der Pauw Hall measurements indicate an implant activation of 36%, which is similar to the value obtained for the conventional furnace annealing at 1,600 C. Good lattice quality restoration was observed in the Rutherford backscattering and photoluminescence spectra.