Properties and annealing stability of Fe doped semi‐insulating GaN structures

Abstract

The properties of semi-insulating GaN films doped with Fe are reported. The 300 K sheet resistivity of the films is 2 x1010 Ω/square with an activation energy of the dark conductivity of 0.5 eV. The Fermi level is also pinned at E C -0.5 eV. The concentration of the 0.5 eV traps in the Fe doped portion of the films was 3 x10 16 cm -3. Also present is a high concentration of deeper electron traps with the level near E C -0.9 eV and of hole traps with level near E V +0.9 eV. Intra-center transitions of the Fe 3+ center are observed in the photoluminescence spectra. The stability of the films were studied after rapid thermal annealing (RTA) at temperatures 750-1050 o C and furnace annealing in hydrogen at temperatures up to 850 o C. The Fe is distributed nonuniformly, with a minimum near 0.5-1 µm from the surface. RTA at 850 o C leads to roughness of the surface and decreases of the sheet resistivity and the cathodoluminescence intensity. The density of deep traps also greatly decreases. The effect becomes much more pronounced for furnace annealing in hydrogen for times on the order of 15 minutes and 850 o C is the highest practicable under these conditions without destroying the surface morphology.

Deep traps in GaN-based structures as affecting the performance of GaN devices

“…Thus, the spectroscopic measurements place the CT Fe 3+ /Fe 2+ level in the vicinity of E c À0.6 eV, in agreement with results reported in Ref. [160][161][162][163][164].…”

“…The electrical properties were shown to be reasonably stable upon annealing, with the decrease of sheet resistivity by about an order of magnitude occurring only after rapid thermal annealing (RTA) at temperatures exceeding 950 8C or after prolonged furnace annealing at 850 8C. These changes were accompanied by the decrease in the magnitude of the PICTS signals due to the 0.9 eV electron traps and 0.9 eV hole traps [163,164]. The presence of the long tails in Fe doping profiles in MOCVD GaN even after the termination of intentional Fe doping reported in Ref.…”

“…The 3 mm-thick films studied in these papers were grown in such a way that only the 0.5 mm layer adjacent to the sapphire substrate was heavily (up to the concentration $10 19 cm À3 according to SIMS [164]) doped with Fe, the rest of the film not doped intentionally, but still showing a relatively high density of Fe, gradually falling down away from the substrate, but showing a build-up to high concentration near the surface. Still, the overall sheet resistivity was quite high, over 10 7 V/square, the material showed a well defined PL 1.3 eV PL band attributable to Fe 3+ internal transitions [162][163][164]. The electrical properties were shown to be reasonably stable upon annealing, with the decrease of sheet resistivity by about an order of magnitude occurring only after rapid thermal annealing (RTA) at temperatures exceeding 950 8C or after prolonged furnace annealing at 850 8C.…”

“…Detailed studies of the electrical properties of GaN:Fe films prepared by MOCVD were reported in Refs. [161][162][163][164]. It was shown that the Fermi level in these layers was pinned near E c À(0.5-0.6) eV level believed to be due to the Fe induced centers.…”

“…It was shown that the Fermi level in these layers was pinned near E c À(0.5-0.6) eV level believed to be due to the Fe induced centers. Other deep traps detected in photoinduced current transient spectroscopy (PICTS) were electron traps with activation energies near 0.12 eV, 0.15 eV, and 0.9 eV, and hole traps with activation energy close to 0.9 eV [161][162][163][164]. The 3 mm-thick films studied in these papers were grown in such a way that only the 0.5 mm layer adjacent to the sapphire substrate was heavily (up to the concentration $10 19 cm À3 according to SIMS [164]) doped with Fe, the rest of the film not doped intentionally, but still showing a relatively high density of Fe, gradually falling down away from the substrate, but showing a build-up to high concentration near the surface.…”