Structure and luminescence of GaN layers T. Barfels a , H.-J. Fitting a,* , J. Jansons b , I. Tale b , A. Veispals b , A. von Czarnowski a , H. Wulff c a Physics Department, University of Rostock, Universita Ètsplatz 3, D-18051 Rostock, Germany b Institute of Solid State Physics, University of Latvia, 8 Kengaraga Street, LV-1063 Riga, Latvia c Institute of Chemistry, University of Greifswald, Soldtmannstr. 23, D-17489 Greifswald, Germany Abstract GaN ®lms grown on h111i Si substrate by means of low pressure MOCVD technique in a horizontal ¯ow quartz reactor arecharacterizedbydifferentthinlayeranalysismethods.ThepolycrystallinehexagonalstructureoftheGaNlayershasbeen checked by means of grazing incidence X-ray diffractometry and IR spectroscopy. Cathodoluminescence CL) spectra and their time kinetics are studied. The mean decay time of the 3.44 eV UV bound exciton transition is below 1 ns, whereas the 3.26 eV violet band shows a slow hyperbolical decay over about 1 ms. A third yellow band appears at 2.12 eV due to transitions via localized states. # 2001 Elsevier Science B.V. All rights reserved. PACS: 81.05 Ea; 78.66 Fd; 78.60 Hk; 78.30 Fs Keywords: GaN layers; MOCVD; Crystal structure; Cathodoluminescence; Luminescence decay time 1. Introduction The group-III-nitride compound semiconductors have attracted attention due to special applications such as blue/UV light emitting diodes LED), laser diodes, solar blind photodiodes PD), high-tempera- ture/high-powerelectronicdevices[1].Besidesmole- cularbeamepitaxyMBE)themetalorganicchemical vapor deposition MOCVD) of GaN ®lms has turned out as the growth method with preference for com- mercialfabrication.Therefore,inRigawehaverebuilt aSi-CVDequipmenttoaMOCVDreactorinorderto growGaNlayersunderdifferentconditionsonvarious substrates.Theaimofthepresentpaperistoprovethe layer morphology and the luminescence quality by appropriate methods. 2. Experimental The GaN ®lms were grown in a horizontal quartz reactor.Apro®ledgraphitesusceptorplatewasplaced inside of the reactor in a distance of 25±30 cm from the right steel end-¯ange. The right end-¯ange is equipped by two one-over-the-other placed and hor- izontallyadjustablegasinputpipesallowingtochange the distance between susceptor and gas source tubes. The gas exhaust is maintained through the left end- ¯angeofthereactor.Twowaferscanbeplacedonthe susceptor.TheheatingisperformedbyaHFinductor 10 kHz, 50 kW). The susceptor temperature can be Applied Surface Science 179 2001) 191±195 * Corresponding author. Tel.: 49-381-498-1646; fax: 49-381-498-1667. E-mail address: hans-joachim.fitting@physik.uni-rostock.de H.-J. Fitting). 0169-4332/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0169-433201)00278-1