Plasma-induced effects on the thermal conductivity of hydride vapor phase epitaxy grown n-GaN/Sapphire (0001)

We have measured high spatial/depth resolution (2-3 μm) thermal conductivity (κ) at 300K before and after plasma-induced effects on a series of n-GaN/sapphire (0001) samples fabricated by hydride vapor phase epitaxy (HVPE) using a ThermoMicroscope's scanning thermal microscope (SThM). The sample thicknesses were 50 ± 5 μm and the carrier concentrations ∼ 8 × 10¹⁶ cm^-3, as determined by Hall effect measurements. The thermal conductivity before treatment was found to be in the 1.70 - 1.75 W/cm-K range, similar to that previously reported for HVPE material with this carrier concentration and thickness [D. I. Florescu et al., J. Appl. Phys. 88, 3295 (2000)]. The samples were processed under constant Ar gas flow and pressure for a fixed period of time (5 min). The only variable processing parameter was the DC bias voltage (125 - 500 V). After the initial 125 V procedure κ exhibited a decrease linear in the DC voltage in the investigated range. At 125 V the thermal conductivity was only slightly less (κ ∼ 1.65 W/cm-K) than the untreated case. κ had dropped to ∼ 0.3 W/cm-K for the 500 V situation. The implications of these results for device applications in the area of high power opto-electronics and high power electronics will be discussed.