Electronic characteristics of Au/Al xGa 1− xN structures grown with various x values

Abstract

We have studied the growth characteristics of Al x Ga 1− x N/GaN and electronic properties of Au/Al x Ga 1− x N structures grown by the MOCVD variation of x. The Al x Ga 1− x N layers were grown on undoped GaN/sapphire (0 0 0 1) epitaxial layers in a horizontal MOCVD reactor at a reduced pressure of 300 Torr. Al composition, x in Al x Ga 1− x N/GaN determined by DCXRD are 0.12, 0.15, 0.19 and 0.2, respectively. Nevertheless, enough feeding of TMA (trimethylaluminum) source during the growth at 300 Torr and 1070°C, the mole fraction x in Al x Ga 1− x N did not increase any more above 0.2. The FWHMs of the DCXRD for (0 0 0 2) diffraction from Al 0.12Ga 0.88N, Al 0.15Ga 0.85N, Al 0.19Ga 0.81N and Al 0.2Ga 0.8N are 450, 469, 502 and 474 arcsec, respectively. While the carrier concentration of Al x Ga 1− x N layers increases, the mobility decreases with the increase of Al mole fraction x. After fabricating Au/Al x Ga 1− x N Schottky diodes, electronic properties of the structures were evaluated by I– V measurement as a function of x. The breakdown voltages of Au/Al x Ga 1− x N diodes at reverse bias mode were in the range of 2.5–15 V. And, the turn on voltages at forward bias mode were in the range of 0.5–5.0 V with the variation of x from 0.12 to 0.19. While Au/Al x Ga 1− x N diodes having low mole fraction of Al showed relatively good rectifing behaviors, the samples having high x exhibited very leaky I– V behaviors. The current density–voltage ( J– V) characteristics at forward bias mode were also evaluated as a function of carrier concentrations which are directly related to x. From each curve of ln ( J) vs. V, I yielded the effective barrier heights ( Φ B ) ranging from 0.6 to 0.78 V, and the ideal factor ( η ) is in the range of 2.7–3.5. The barrier heights obtained in this work are close to each other, but the ideal factors are slightly different.