Figures

Figure 1

Simplified scheme of GaN growth by Sublimation Sandwich Technique.

Figure 2

Photo of GaN crystal grown on a sapphire substrate by the sublimation technique. The thickness of the crystal is 0.3 mm. The dark area in the center of the crystal is attributed to Ga droplets accumulated at the interface between sapphire and GaN. The appearance of the droplets at the initial stage of growth is related to lowering of V/III ratio over the substrate from the periphery to the center.

Figure 3

Distribution of ammonia concentration in the reactor of vertical configuration during sublimation growth of GaN. The color transition from blue to red indicates increasing ammonia mass fraction from 0.15 to 1.00. The substrate temperature is 1150°C, the temperature difference T = 50°C.

Figure 4

Typical temperature distribution in the reactor of vertical configuration during sublimation growth of GaN (the substrate temperature is 1150°C, and temperature difference T = 50°C).

Figure 5

Streamlines of the gas flow in the reactor calculated for typical growth conditions (the substrate temperature is 1150°C, and the temperature difference T = 50°C).

Figure 6

Concentration distributions of main gaseous species in the growth cell during sublimation growth of GaN. The color transition from blue to red indicates increasing species mass fraction (from 8.6·10-4 to 7.9·10-3 for gallium, from 0.15 to 0.73 for ammonia, and from 0.26 to 0.98 for hydrogen). The substrate temperature is 1150°C, the temperature difference T = 50°C.

Figure 7

Growth rate versus clearance between the source and substrate measured for GaN crystals grown on sapphire.

Figure 8

Gallium flux from the source to the substrate calculated for different evaporation modes and measured experimentally.

Figure 9

GaN growth rate versus temperature calculated for the sandwich system (solid lines). Blue circles are the experimental data obtained for these growth conditions. The red arrow indicates maximum growth rate achievable for the chosen T and reactor pressure, limited only by Ga transport.

Figure 10

Schematic plot of the "growth window" related to Sublimation Sandwich Technique (reactor pressure is 1 atm).

Figure 11

Color CL images of GaN crystals grown (a) directly on sapphire substrate, (b) on MOVPE layer (~5 µm thick), and (c) on SiC(0001) Si-faced surface.

Figure 12

Photoluminescence and CCL-SEM characterization of GaN crystals grown by SST: (a) typical room-temperature emission spectrum of GaN grown on SiC(0001) Si-faced surface, (b) CL image of GaN surface far from defect area, (c) CL image of GaN surface near the defect area, (d) CL image of surface of GaN grown under non-optimal conditions.

Figure 13

Temperature dependence of EPR spectra of GaN crystal grown on 6H-SiC(0001) Si-faced substrate. The spectra exhibit a hysteresis upon heating-cooling process that is an evidence of metastable defect formation.

© 1998 The Materials Research Society