P-type GaN epitaxial layers and AlGaN/GaN heterostructures with high hole concentration and mobility grown by HVPE
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E8.28.1
P-type GaN epitaxial layers and AlGaN/GaN heterostructures with high hole concentration and mobility grown by HVPE A. Usikov1, O. Kovalenkov1, V. Ivantsov1, V. Sukhoveev1, V. Dmitriev1, N. Shmidt2, D. Poloskin2, V. Petrov2, V. Ratnikov2 1 Technologies and Devices International, Inc., 12214 Plum Orchard Dr., Silver Spring, MD 20904, U.S.A. 2 A.F. Ioffe Physico-Technical Institute of Russian Academy of Science 26, Polytekhnicheskaya , 194021, St.-Petersburg, Russia. ABSTRACT In this paper we report p-GaN growth by hydride vapor phase epitaxy (HVPE) on sapphire substrates. Mg or Zn impurities were used for doping. Layer thickness ranged from 2 to 5 microns. For both impurities, as-grown GaN layers had p-type conductivity. Concentration NA-ND was varied from 1016 to 1018 cm-3. An annealing procedure at 750oC in argon ambient typically increased the concentration NA-ND in 1.5-3.5 times. For Mg doped GaN layers, room temperature hole mobility of 80 cm2V-1s-1 was measured by conventional Van Der Pau Hall effect technique for material having hole concentration of about 1x1018 cm-3. Initial results on highly electrically conducting p-type AlGaN/GaN heterostructures doped with Zn are also reported. INTRODUCTION Hydride vapor phase epitaxy (HVPE) currently is the only epitaxial method capable to produce GaN, AlN, and AlGaN materials with a growth rate sufficiently high for the formation of thick layers and substrates. High quality of such thick layers and free-standing GaN wafers has been recently demonstrated by several research teams including substrate applications of HVPE grown materials for GaN-based power devices [1], high-frequency transistors [2], and blue lasers [3]. Other epitaxial methods like metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) have growth rates approximately 100 times less than the HVPE method does and are not practical for fabrication of thick GaN, AlN, and AlxGa1-xN layers. Recently first HVPE grown p-type GaN layers and AlGaN/GaN pn structures have been demonstrated [4,5]. These results indicate a possibility to fabricate thick p-type GaN layers and possibly p-type GaN substrates by HVPE. Thick p-type GaN layers with low electrical resistivity grown on sapphire can be potentially used as substrates providing close lattice matching to AlGaN-based device structures. Highly doped thick p-type GaN layers and AlGaN/GaN heterostructures may lead to novel device and contact metallization designs for GaN-based light emitters and electronic bipolar devices. In this paper we report p-type GaN layers and GaN/AlGaN heterostructures grown by HVPE technology and results of samples characterization. EXPERIMENTAL DETAILS
E8.28.2
GaN layers and AlGaN/GaN heterostructures were grown using multi-wafer HVPE growth machines constructed and built at TDI. The HVPE growth machines were equipped with an atmospheric-pressure horizontal hot-wall quartz reactor and two-zone resistively heated furnaces. Samples were grown at 1050oC using Ga and Al metals as metallic source materials
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