Magnetic and Optical Properties of Mn-doped Gan Thin Films and P-i-n Devices

In this paper, we report on the growth and characterization of single crystal GaMnN thin films and p-i-n junction devices grown by metal-organic chemical vapor deposition (MOCVD). Single crystal GaMnN films were achieved by optimizing the growth temperature, growth rate and the Mn:Ga gas phase ratio. A growth window for obtaining single crystal Ga1-xMnxN with 0.006≤x≤0.023 was found within a temperature range of 850oC<TG<1040oC, as determined by transmission electron microscopy (Reed et al., 2001). Temperature dependent superconducting quantum interference device (SQUID) measurements confirmed the absence of superparamagnetism and spin glass behavior within the films and identified Curie temperatures between 228K and 500K for GaMnN. It was found that the magnetic properties of MOCVD grown GaMnN are markedly affected by intentional introduction of donor or acceptor states into the film. Si or Mg co-doping of GaMnN films led to either ferromagnetic or paramagnetic behavior depending on the concentration. The magnetic properties of the GaMnN material system correlates with the Fermi level. Ferromagnetism was observed only when the Fermi energy level was near to the Mn energy band resulting in a partially occupied Mn energy level; a prerequisite for conduction within this band. The presence of the Fermi energy level within the Mn energy band allows the presence of carriers that mediate ferromagnetism. These results further confirm that the ferromagnetic properties result from a solid solution of Mn in the GaN and not from the presence of secondary phases, clusters, or precipitates, or secondary phases. In addition to co-doping, the dependence of ferromagnetic properties of GaMnN films on carrier transfer across heterojunctions layers was also studied. The magnetic properties of GaMnN, as a part of GaMnN/GaN:Mg heterojunctions depend on the thickness of both the GaMnN film and the adjacent GaN:Mg layer. These results are explained based on the occupancy of the Mn energy band and how this occupancy is altered by carrier transfer at the GaMnN/GaN:Mg interface. GaMnN p-i-n junction devices were also fabricated to study the effect of the magnetic properties on the I/V characteristics. These devices consist of nGaN:Si/i-GaMnN/p-GaN:Mg layers grown by MOCVD. The carrier concentrations for the n and p-type layers are ~5 X 10/cm and 1 X 10/cm respectively. The GaMnN layer is approximately 0.1 – 0.2 μm thick with up to 1% Mn. The device pattern consisted of interdigitated fingers with a footprint of 400 μm X 400 μm. SQUID measurements of these devices show that the ferromagnetic properties were maintained during processing. Electroluminescence measurements for these devices showed visible emission at room temperature at ~ 410-430 nm. Eventually, it may be possible to combine electronic, magnetic, and optical functions on a single IIINitride chip for novel applications.