AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP8
Scanning Tunneling Microscopy Study of GaCrN Grown by MBE

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: M.B. Haider, Ohio University
Authors: M.B. Haider, Ohio University
H.A. Al-Brithen, Ohio University
R. Yang, Ohio University
C. Constantin, Ohio University
D. Ingram, Ohio University
A.R. Smith, Ohio University
Correspondent: Click to Email
According to Sato et al., (Ga,Cr)N is expected to show ferromagnetism above room temperature if the bulk Cr@sub Ga@ concentration is above 2%.@footnote 1@ Although many (mainly bulk) techniques have been applied to study dilute magnetic nitride systems here we apply in situ STM to investigate issues of Cr incorporation, Cr diffusion/segregation, and the effects of growth parameters. Cr-doped GaN(000-1) has been grown using rf-plasma MBE on sapphire (0001) at Ts ~ 700°C. The Ga/N flux ratio has been varied from 65-100% with variable Cr/Ga flux ratio between 3-11% for GaCrN growth. Based on the Ga/N flux ratio, three growth regimes were found: N-rich, metal-rich, and Ga-rich. It was found that under all three conditions GaCrN surfaces are smoother even to atomistic level forming 3x3 reconstructions after the growth as revealed by RHEED and AFM. This is in contrast to Ga-polar GaMnN case, where N and metal-rich surfaces are not smooth and under Ga-rich conditions Mn droplets of micron size are formed due to the Ga bilayer which exists during Ga-rich GaN(0001) growth.@footnote 2@ Atomic scale STM images of Ga-rich GaN(000-1) covered with 0.05ML of Cr deposited at 700°C show 3x3 and 6x6 reconstructions indicating the presence of Cr atoms within the surface structure. STM images of GaN(000-1) with Cr deposition of 0.2ML and above show some linear features suggesting transition from Cr substitution to 2nd order phase nucleation at the surface. The 3x3 reconstructions have been observed upon exposure of GaN(000-1) 1x1 to Cr at room temperature by RHEED and STM. These STM images suggest that on GaCrN surface, at low Cr concentration, Cr occupies Ga position. Another interesting phenomenon of contrast reversal of 3x3 and 6x6 reconstructions has been observed by STM on 5% Cr doped GaN(000-1) surface, which depends on the tip condition. @FootnoteText@ @footnote 1@Sato et al. J. Superconduc, 16 (2003) 31@footnote 2@Haider et al. J. Appl. Phys., 93 (2003) 5274.