Low-resistance Ni-based Schottky diodes on freestanding n-GaN

Abstract

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Free-standing gallium nitride Schottky diode characteristics and stability in a high-temperature environment

“…The apparently significant thermionic field emission effect from the temperature-dependent diode ideality analysis can be correlated with the high reverse leakage current density, which is 2-3 greater than we have previously measured for similar diode structures on-wafer (i.e. no packaging) [15]. Although the reason for a dominant TFE mechanism is unclear at this point, it is interesting to note that the extracted kT /qE 00 ratio is lower than expected from the theoretical expression for the nominal epi-doping level in these diodes (N d = 1 × 10 17 cm −3 ) [19]:…”

“…High leakage currents also have previously been attributed phonon-assisted tunnelling (third part in [25]), though this effect appears to be more pronounced at higher reverse voltages and higher temperatures, whereas for our diodes the leakage appears to saturate with both reverse voltage and temperature (figures 3(b) and 4(b)). In our case, it seems that the most dramatic effect on the leakage current takes place after the Schottky contact fabrication step, possibly during the thermo-compression bond (die attach) stage, given the low leakage observed in our previous on-wafer tested diodes [15]. We are currently investigating the effect of thermal annealing on the Ni-GaN interface and the resulting current-voltage characteristics, though at this point it seems that recovery of the barrier can be achieved by optimized annealing conditions, as indicated by the increase in barrier height after long-term storage at high temperature (figure 7).…”

“…Electrically biased high-temperature long-duration (HTLD) storage was carried out under N 2 at 300 • C with 0.1 A forward bias current or with −3.5 V reverse bias voltage for up to 466 h. For future reference herein, the forward current biased storage and reverse voltage biased storage conditions are denoted by FCBS and RVBS, respectively. IV measurements were made on diodes before and at various intervals (15,112,162, 348 and 466 h) during the HTLD storage period. An additional non-biased storage test was carried out under N 2 at temperatures of 350 • C and 400 • C for 1007 h and 120 h, respectively.…”

“…While these results are promising for high-temperature device development, these diodes were fabricated using highresistivity FS-GaN, whereas low-resistivity substrates with a suitably low doped epi-layer are needed to ensure low series resistance and, ultimately, a low forward voltage under highcurrent operation [14]. We have previously reported very low specific 'on-resistance' (<0.6 m cm 2 ) for Ni-based Schottky diodes using a low-resistivity FS-GaN substrate with a thin lowly doped epi-layer [15], but the stability of this type of diode structure under long-term electrically biased storage has not been established. Here we report on the reliability of these devices, under extensive long-term electrically biased and unbiased storage conditions at temperatures between 300 • C and 400 • C and for durations up to 1000 h in nitrogen or 1500 h in air.…”