SEM photograph of GaN localized islands on the patterned Si_xN_y mask with growth times of 5min. The growth temperature was 1080°C with 16µMole/min TMGa flow.

SEM photograph of GaN localized islands on the patterned Si_xN_y mask with growth times of 10min.

SEM photograph of GaN localized islands on the patterned Si_xN_y mask with growth times of 20min. At this stage, the GaN pyramids are delimited by six facets {101} and a top C(0001) facet.

SEM photograph of GaN localized islands on the patterned Si_xN_y mask with growth times of 30min. After a such growth time, the top C(0001) facet is vanished.

Measurements vs. growth time of the different characteristic dimensions of the hexagonal pyramid. Lines labeled 1 to 3 are regressions through the measured values. From these slopes, the growth rates V_C and V_R in the C and R direction were estimated to be 13 and 2.1 µm/h respectively. The growth temperature was 1080°C with 16µMole/min TMGa flow.

Cross section perpendicular to the (11-20) direction of a localized GaN truncated hexagonal pyramid shown in figure 1(c). W_T and W_B were respectively the width of the top facet and bottom base; H was the height of the pyramid. W_T, W_B and H were function of the growth duration t. _R was the angle between (0001) and ((101) delimiting planes. W_B0 was the width of the aperture in the Si_xN_y mask.

SEM photograph of GaN localized islands grown on the patterned Si_xN_y mask with [Mg]/[Ga] mole ratios of 0 (undoped GaN pyramids). Except for the Mg introduction, the growth conditions (temperature 1080°C, TMGa 16 µMole) and time (30') were identical for both samples.

SEM photograph of GaN localized islands grown on the patterned Si_xN_y mask with [Mg]/[Ga] mole ratios of 0.08.

SEM photograph of GaN localized islands grown on the patterned Si_xN_y mask with [Mg]/[Ga] mole ratios of 0.11.

SEM photograph of GaN localized islands grown on the patterned Si_xN_y mask with [Mg]/[Ga] mole ratios of 0.14. The V_R/V_C is about 4.

Growth rate vs. Magnesium to Gallium precursor mole ratio in the vapor phase deduced from measurements on SEM plan view and cross section of hexagonal pyramids as shown on figure 3. Lines were guides for eyes.

SEM photographs of high Si-doped GaN localized islands. The growth conditions were : SiH₄ 0.20µMole, temperature 1080°C, TMGa 40µMole and growth time 30'.