Annealing Study of Ion Implanted MOCVD and MBE Grown GaN
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Table I. Implanted ion species including the implantation energy and dose. The peak range and peak concentration were calculated using the PROFILE Code [6]. Range (A)
3 Peak Cone. (cm )
2211
2.6x 1019
5xl 104
3035 3339
7.4x 10 5 , 2.7x 1019 1.6xl 109
200
5x 10' 3
4270
1.5x 108
390
1x10'14
4990
3.1x 1018
4
4203
3.3x 1018
2 Dose (CM- )
Species
Energy (keV)
Ar
390
Mg
300
2.2x 10 4, 8.2x 1014
Si
390
Be C 0
390
4
5x 10'
Ixl10
RESULTS AND DISCUSSION
Wavelength (nm) Low temperature PL of unimplanted 450 400 700650 600 550 500 350 GaN annealed in NH 3 and N 2 revealed II I I I I I significant changes in luminescence due to 1050 *C The NH 3 annealed samples annealing. showed a distinct increase in donor-acceptor pair (D-A) emissions as annealing temperature was increased as shown in Figure 1. Sample Annealed Unimplanted However, all of the annealed samples showed 90 .I K in CA LMOCVD PL @2min NH3 a factor of 2 to 3 drop in exciton intensity 0 compared to their unannealed counterparts. 100 *C The yellow peak intensity also dropped by a factor of 2 for the highest anneal temperatures. Samples annealed in N 2 at the C same temperature and for the same annealing t-J C. time show only a decrease in overall 0luminescence by a factor of about 2. No increase in the D-A peak intensity was found for N 2 annealing. Absorption measurements 600 .C of the bandedge show almost no change in slope with annealing for 90 minutes at 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 temperatures ranging from 600 to 1050 'C. Photon Energy (eV) Argon is an inert element, and was therefore implanted into GaN to study the damage created by implantation and its Figure 1. Photoluminescence of as-grown, MOCVD GaN samples annealed inNH3 for 90 min at temperatures subsequent annealing. In contrast to earlier of 600 to 1050 'C. reports [1,2], the Ar implanted samples did not show any unique PL peaks. In all Ar implanted and annealed samples, the D-A band dominated the spectrum. The PL peaks in the NH 3 annealed sample were better resolved than the N 2 case. However, the absorption edge showed identical damage recovery for both N 2 and NH 3 annealing. Near the bandedge, the absorption data revealed an exponential tail of states. The length of which could be characterized by an energy E0, which is given by .
814
.
I
1/E0 =d(lncc)/d(hv) [7]. Here oc is the absorption coefficient, and hv is the incident photon energy. The room temperature absorption edge of the Ar-
Implanted, Unannealed E =66.7meV
implanted MOCVD GaN is shown in A
800* C Anneal 34.2 meV
" C,
._J
*
anneal showed significantly increased
900' C Anneal " 30.7 neVy
at longer wavelengths absorption compared to lower anneal temperatures. Identically prepared samples annealed in N 2 gave values of E0 = 34.7 meV for the 800 'C anneal and 29.4 meV for the 1000°C anneal which compare very
A
1050' C Anneal .
closely with the values for the NH3 anneals.
As-Grown
22.7 meV
0
Figure 2. The longest tail was observed in the as-implanted material, and a steady decrease i
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