Luminescence Properties of As, P, and Bi as Isoelectronic Traps in GaN
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Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998 Materials Research Society
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EXPERIMENTAL RESULTS AND DISCUSSION.
In our studies we used a sample cut from a single crystal of GaN epitaxial wafers grown by MOCVD on the basal plane of sapphire substrates. The GaN wafers were high quality n-type with thicknesses and carrier concentrations as follow: for samples # 11 GaN-EMCORE 1.3 •tm and 2 ×1017, for samples #5 GaN -CREE 1.8 jitm, and 2× 1016. The wafers were implanted at room temperature with P+ and Bi÷ ions with a dose of 5× 10'4 ions/cm 2 at 200 keV, sample #11, samples #5 with dose of 1× 1014 ions/cm2 ions/cm2 at energy 200 keV. The As+ were implanted sample # 12 with a dose of 1x io101 2 at 200 keV, with a dose of6.5x×1012 ions/cm at 120 keV and with a dose of3xli0'3 ions/cm2 at 50 keV. The implanting ion beam was inclined at 70 to the normal to the GaN epilayers to prevent channeling. The simulated depth profile, has the projected range for P+ at 167.3 nm, Bi÷ at 305 nm, and As at 600 nm from the surface and a peak concentration of 3.31 x 1019 cm-3 , 4.55x 1019 cm"3, and 3
2.45× 10'9 cm- respectively. Post implant annealing (an.) at temperatures of up to 1150 °C and at
different duration of time was done in a tube furnace under flowing NH 3 or N2, and in a rapid thermal annealing system in ambient of N2 using the proximity cap method to recover implantation damages. The improved crystal quality of GaN was conformed by Raman spectra and visually apparent because the samples which had turned 'milky' after the ions implantation regained their transparent appearance following annealing. The PL of GaN: P showed a strong emission peaked at 423 - 428 nm with modulated structures that depend on annealing conditions (Fig. 1, 2). The PL of GaN: Bi shows a modulated luminescence spectrum Fig.3 observable at temperatures ranging from 9 K to 300 K (due to interference effect). Figures 4 and 5 show PL spectra taken at a series of temperatures from GaN implanted with As and annealed at1 100 °C during 0.5 h in flowing NH 3 and N2 respectively. The emission spectra differed in intensity and shape. A sample annealed in NH3 shows about a 2.6 times stronger peak at 476 nnm than a sample annealed in N2 under this same excitation condition. The emission spectra from GaN: As exhibited a double band structure which peaked at 460 nm and 476 nm at 9 K. The PL of GaN: P annealed at 1150 0C in NH-3 exhibits strong pair-type luminescence transitions overlapped with an emissions band of an exciton bond to the P isoelectronic trap which became dominant at 150 K (Fig. 1). From Fig. 1 we obtained experimental evidence that under the above bandgap excitation, there exists the pair-type emission involving P isoelectronic traps and neutral donors and the emission band due to the recombination of excitons bound to phosphorus isoelectronic traps. With increasing temperature the pair emission decreased and vanished at 175 K, but the emission of excitons bound to a P isoelectronic trap is observed up to room temperature. The new pair spectra are diffe
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