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Rensselaer Polytechnic Institute Troy, NY 12180 ** Crystal IS, Inc. Latham, NY 12110

ABSTRACT Large (up to 10mm diameter) aluminum nitride (AlN) boules have been grown by the sublimation-recondensation method to study the preparation of high-quality single crystal substrates. The growth mechanism of the boules has been studied using AFM. It has been determined that large single crystal grains in those boules grow with a density of screw dislocations below 5×104 cm-3 while edge dislocations are at lower density (none were observed). High-quality AlN single crystal substrates for epitaxial growth have been prepared and characterized using Chemical Mechanical Polishing (CMP) and AFM imaging, respectively. Also, the differential etching effect of KOH solutions on the N and Al-terminated faces of AlN on vicinal c-faces has been investigated. In order to identify the N or Al-terminated face, convergent beam electron diffraction has been used. INTRODUCTION Single crystal AlN is attractive for the fabrication of substrates for III-nitride epitaxial growth. Applications of wide-bandgap and high-temperature semiconductors include the development of blue/UV solid-state charge injection lasers, UV optical sources and detectors, high power microwave devices, high power switches, and high temperature applications. Enhanced III-nitride epitaxy on AlN substrates, due to smaller lattice mismatch, smaller thermal expansion mismatch and good chemical compatibility, may allow substantial improvement in the ability to manufacture these devices. In addition, very low defect material is needed for developing solid-state low noise and power devices for use in power supplies, communications, fire control, surveillance, and multifunctional RF systems using the nitride, wide-bandgap semiconductors. Foreign substrate induced defects have also been implicated in the performance of high power microwave devices. Substrates of AlN are also attractive for surface acoustic wave (SAW) applications, which would take advantage of the very high sound velocity in AlN. This would have application in high power, high frequency amplifiers for wireless communication base stations. The high thermal conductivity and electrically insulating properties of AlN are also attractive for high performance substrates where heat sinking is a key issue. +

Currently at the University at Albany, NY 12222

F99W6.7

For III-nitride epitaxial growth, the preparation of nearly-atomically flat surface is required. Due to the extreme hardness of AlN, we have found that epitaxial-growth quality surfaces can be only achieved by using chemical-mechanical polishing (CMP) methods. The determination of the etching properties of single crystal substrates is of great importance for epitaxial growth and device preparation. We have studied the effects of KOH solution on the both the N and Al-terminated surfaces along the c-axis crystallographic direction on high-quality single crystal substrates. Also, we discuss a TEM-based method to unambiguously identify the N and Al-terminated fac