Plasma-Induced Effects On The Thermal Conductivity of Hydride Vapor Phase Epitaxy Grown n -GaN/Sapphire (0001)
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Plasma-Induced Effects On The Thermal Conductivity of Hydride Vapor Phase Epitaxy Grown n-GaN/Sapphire (0001) D.I. FLORESCU*, FRED H. POLLAK*, WILLIAM B. LANFORD**, FARID KHAN**, I. ADESIDA**, and R.J. MOLNAR*** * Physics Department and New York State Center for Advanced Technology in Ultrafast Photonic Materials and Applications, Brooklyn College of CUNY, Brooklyn, NY 11210 ** University of Illinois at Urbana-Champaign, Urbana, IL 61801 *** Massachusetts Institute of Technology, Lincoln Laboratory, Lexington, MA 02420
ABSTRACT 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 ~ 8x1016 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.
INTRODUCTION Ion beams are broadly used in the semiconductor industry for a wide range of processing steps, such as dopant implantation, implant isolation, dry etching, and material characterization [1]. Lattice disorder is always a simultaneous effect of ion bombardment. Relatively few studies have been reported on ion-beam-induced damage in GaN [2-4]. GaN (and other group III-nitride semiconductors) has attracted considerable attention in recent years for applications to high power electronic and opto-electronic devices, including blue/green light emitting diodes (LED), lasers, and solid-state transistors. These uses require high power capability making thermal behavior, particularly thermal conductivity an extremely important material property. However, despite the large body of work, both experimental and theoretical on the electronic, optical, and structural properties [5] of the group III nitrides relatively little work has been reported on
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thermal conductivity measurements [6-11] or theory [12-14]. This quantity is of importance from both fundamental and applied perspectives. The lattice thermal conductivity is a function of the mean free path of the phonons and hence is determined by both intrinsic (phonon-phonon Umklapp scattering) and extri
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