Figures

Figure 1

GaN growth rate as a function of the Ga flux (Beam Equivalent Pressure) for a fixed substrate temperature (750°C) and amount of active nitrogen. Definition of the stochiometry zone (ie. III/V ratio ~1).

Figure 2

Cross sectional SEM photographs of GaN layers grown with different III/V ratios, from N-rich conditions (sample A) to close to stoichiometry (sample D).

Figure 3

Low temperature PL spectra of the samples described in Figure 2.

Figure 4

Top view SEM photographs of three different zones on a type-B sample, from the edge of the wafer towards the center. Notice the decrease in the density of columnar microcrystals.

Figure 5

Low temperature PL of the three zones described in Figure 4, from the edge to the center of the wafer.

Figure 6

Cathodoluminescence imaging of a type-B sample for two energies : a) 3.454 and b) 3.473 eV.

Figure 7

Top views SEM photographs of three different type-C samples exhibiting different microcrystals densities on the surface.

Figure 8

Low temperature PL of the three samples described in Figure 7.

Figure 9

Cathodoluminescence of a type-C sample with electron beam energies from 5 to 25 keV (ie different excitation depths).

Figure 10

Calculated excitation depth as a function of electron beam energy for GaN

© 1998 The Materials Research Society