Rare-Earth Doped Gallium Nitride (GaN)- An Innovative Path Toward Area-scalable Solid-state High Energy Lasers Without Thermal Distortion

Abstract

Sensors and Electron Devices Directorate, ARLApproved for public release; distribution unlimited. ii REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)April 2009 ARL-TR-4794 SPONSOR/MONITOR'S ACRONYM(S) 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution unlimited. SUPPLEMENTARY NOTES ABSTRACTWe have demonstrated, for the first time, in situ neodymium (Nd) doping of gallium nitride GaN by plasma-assisted molecular beam epitaxy (PA-MBE). The Nd doping is controlled by the GaN growth conditions and the Nd effusion cell temperature. The Rutherford backscattering spectroscopy (RBS) and secondary ion mass spectrometry (SIMS) data indicated Nd doping as high as ~8 at. %, with no evidence of phase segregation identified by x-ray diffraction (XRD) for Nd up to ~1 at. %. The Nd incorporation reached a limit while maintaining crystal quality. Strong room-temperature (RT) luminescence corresponded to the three characteristic Nd emission multiplets, with the Stark energy levels resolved by photoluminescence (PL) and photoluminescence excitation (PLE). Although the 4f electrons were well shielded from the host material, we were still able to observe weak electron-phonon interactions. Spectral correlation of the multiplets for above (325 nm) and below (836 nm) GaN bandgap excitation implied enhanced substitutional doping at the Ga site. The highest RT PL intensities corresponded to a doping level between 0.1-1 at. %. The enhanced substitutional doping at the Ga site and low optical loss in waveguide structures suggests GaN:Nd with a high enough Nd concentration has significant potential for use in simple, area-scalable, RT, diode-pumped, solid-state high energy lasers (HELs). SUBJECT TERMSHigh energy laser, thermal conductivity, GaN, Nd, molecular beam epitaxy, Stark energy level, luminescence SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON