Luminescence related to high density of Mg-induced stacking faults in homoepitaxially grown GaN

The effect of Mg doping on stacking fault (SF) formation in $c$-plane GaN grown by metal-organic chemical-vapor deposition has been studied for Mg concentration between 2 × 10${}^{18}$ cm${}^{-3}$ and 5 × 10${}^{19}$ cm${}^{-3}$. Transmission electron microscopy studies demonstrate a direct correlation between the increasing Mg content and the number of small (3–10-nm long) SFs present. The energy dispersive x-ray analysis (EDX) line profile of a SF shows that the Mg-impurity atom resides at a distance approximately 5 nm from the SF. Cathodoluminescence (CL) mapping reveals that the Mg-doped regions radiate at energies corresponding to known SF emission peaks. SF-related peaks in CL spectra show metastability, which may be attributed to transfer processes involving Mg acceptors and nearby associated SFs.

Figure 1

Cross-sectional TEM images of GaN samples: (a) [Mg] = 5 × 10${}^{19}$ cm${}^{-3}$, (b) [Mg] $=$ 2 × 10${}^{18}$ cm${}^{-3}$, and (c) undoped GaN. The white arrows indicate the position of SFs. The crystallographic direction [0001] is also indicated for each image.

Figure 2

TEM image of PID defects in $p$-type-doped GaN layer with Mg concentration 2 × 10${}^{19}$ cm${}^{-3}$.

Figure 3

TEM image of basal-plane SF in the as-grown sample with [Mg] $=$ 5 × 10${}^{19}$ cm${}^{-3}$.

Figure 4

(a) EDX-line profile of Mg concentration in as-grown sample with [Mg] $=$ 5 × 10${}^{19}$ cm${}^{-3}$; (b) EDX spectra in the same sample from points 1, 2, and 3 as indicated in the STEM image in (c). The EDX scan was done over a SF as shown by the white line in (c). SF plane and the growth direction [0001] are indicated by arrows.

Figure 5

CL spectra taken at 5 K and Δ$t$ $=$ 0 of Mg-doped GaN films before and after annealing with different Mg concentrations.

Figure 6

CL-spectra transformation during delay time Δ$t$ $=$ 0–30 min at 5 K of Mg-doped GaN films with (a) [Mg] = 6 × 10${}^{18}$ cm${}^{-3}$ and (b) [Mg] $=$ 5 × 10${}^{19}$ cm${}^{-3}$. All spectra are normalized.

Figure 7

(a) SEM and (b)–(f) CL mapping of a TEM sample for the as-grown Mg-doped GaN sample with [Mg] $=$ 6 × 10${}^{18}$ cm${}^{-3}$.

Figure 8

(a) Schematic drawing of the band alignment in the case of basal plane SF. (b) Band profile in the vicinity of the acceptor.