Single-Crystal Aluminum Nitride Substrate Preparation from Bulk Crystals
- PDF / 970,300 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 36 Downloads / 215 Views
Single-Crystal Aluminum Nitride Substrate Preparation from Bulk Crystals J. Carlos Rojo, Leo J. Schowalter*, and Kenneth Morgan Crystal IS, Inc., Latham, NY 12110 Doru I. Florescu and Fred H. Pollak, Brooklyn College, Brooklyn, NY 11210 Balaji Raghothamachar and Michael Dudley SUNY, Stony Brook, NY 11794 ABSTRACT Large (15mm diameter) single-crystal AlN boules have been prepared using sublimationrecondensation growth. X-ray topography shows that the dislocation density averages less than 103 cm2 in some of the substrates but also that the dislocations are not uniformly distributed. Also, strain due to the differential expansion with the crucible walls seems to cause severe cracking in the periphery of the crystal and high-strain regions. Thermal analysis using the Scanning Thermal Microscopy (SThM) reveals a thermal conductivity of 3.4 ± 0.2 W/K-cm, which is the largest value ever reported for AlN. INTRODUCTION Aluminum nitride (AlN) has received attention as a candidate for III-nitride epitaxy applications due to its close lattice match, minimal differential thermal expansion compared to GaN, and high thermal conductivity. There is interest in AlN substrates as a competitive substrate for heteroepitaxial growth of GaN until commercial bulk GaN substrates become available. In addition, AlN is a more desirable substrate than GaN for device structures that require Al-rich nitride epitaxial layers such as solar-blind UV detectors, UV light sources and high power microwave devices. Among the properties that the ideal substrates for III-nitride device fabrication should posses, thermal conductivity plays a role of paramount importance. The next generation of high-power, high-temperature electronic devices will demand a high thermal conductivity substrate capable of dissipating the large amounts of heat generated at the active layers to prevent rapid aging and catastrophic failure. Slack et al. [1] estimated the thermal conductivity of AlN to be 3.19 W/cmK and a more recent study [2] claims the AlN thermal conductivity value to be even higher, approximately 5.9 W/cm-K. In either case however, the value of the thermal conductivity strongly depends on the concentration of oxygen impurities in AlN crystals. Oxygen is able to substitute nitrogen in AlN up to very high concentrations. This substitutional defect has associated an aluminum vacancy, which can be a very efficient center for phonon scattering [3]. Therefore, minimizing oxygen impurities during the growth process is crucial to produce high thermal conductivity AlN substrates. *
on sabbatical from the Physics, Applied Physics and Astronomy Dept., Rensselaer Polytechnic Institute, Troy, NY 12180 E2.1.1
Out of all the techniques used to grow bulk AlN, the sublimation-recondensation technique has been recognized as the most promising method to produce large AlN boules. While the sublimation-recondensation technique, first developed by Slack and McNelly [4], has been known for several decades, not much progress has been achieved in scaling up the process. Even though
Data Loading...