Journal of Crystal Growth 231 (2001) 357–365 GrowthofGaNnanowiresbydirectreactionofGawithNH 3 Maoqi He a,1 , Peizhen Zhou a , S. Noor Mohammad a , Gary L. Harris a , Joshua B. Halpern a, *, Randy Jacobs b , Wendy L. Sarney b , Lourdes Salamanca-Riba b a Materials Science Research Center of Excellence, Howard University, Washington, DC 20059, USA b Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD 20742, USA Abstract Semiconducting,singlecrystalwurtziteGaNnanowireshavebeengrownbydirectreactionofmetalGawithNH 3 in a tube furnace. This paper discusses the growth mechanism. Nanowires grow only between 8251C and 925 o C. Their diametersvarybetween20and150nmanddependdirectlyontemperatureandNH 3 flowrate.Wiresaslongas500 mm have been fabricated; once wires have formed, their length increases directly with time in the reactor. There are three different stages in the process, each of which has its own mechanism. First, a nearly amorphous GaN matrix forms, followed by growth of hillocks of thin GaN platelets. Finally, nanowires emerge from the edges of the platelets in characteristicdirections.ThisanalysiscanbeusedasaguideforcontrollingGaNwirediametersandlengths.Strategies forgrowthofthinnerandthickernanowiresaresuggested.Thickercylindricalstructuresdenotedasrodsgrowfromthe face of the platelets. Description of their growth mechanism requires further study. r 2001 Elsevier Science B.V. All rights reserved. Keywords: A3. Chemical vapor deposition processes; B1. Gallium compounds; B1. Nitrides; B2. Semiconducting III–V materials 1. Introduction Very recently we have grown a large range of semiconducting, single-crystal, cylindrically sym- metric GaN forms without using catalysts [1] and made progress in characterizing these structures andtheirgrowthprocesses[2].GaNnanomaterials have interesting and potentially important appli- cationsasexemplarymaterialstodemonstratenew theoreticalconceptsandforpracticalapplications. The I 2V characteristic of thicker GaN rods (500nm to 10 mm diameter) show them to be semiconductingandUVphotoconducting[3].The promise of these devices for optical/electronic nanoscale switching devices is exciting. Perhaps the most interesting questions require fabrication of smaller diameter nanowires than we have currently been able to grow. Such devices would be wonderful testbeds for studying quantum effectsinone-dimensionalstructures.Ontheother side,growthoflargerdiameterrodscouldbevery useful for optical devices and electronic applica- tions. An interesting first use might be as inter- connects in microelectronic and electro-optical devices. Knowledge of the growth mechanism *Corresponding author. Deparment of Chemistry, Howard University,525CollegeSt.NW,WashingtonDC20059,USA. Tel.: +1-202-806-6883; fax: +1-202-806-5367. E-mail addresses: jbh@scs.howard.edu (J.B. Halpern), mqhe@hotmail.com (M. He). 1 Also at: Chemistry Department, Howard University, USA. 0022-0248/01/$-see front matter r 2001 Elsevier Science B.V. All rights reserved. PII:S0022-0248(01)01466-X