| AVS 59th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing | Thursday Sessions |
| Session EM+TF+AS-ThA |
| Session: | Growth and Characterization of Group III-Nitride Materials |
| Presenter: | J.K. Hite, U.S. Naval Research Laboratory |
| Authors: | J.K. Hite, U.S. Naval Research Laboratory M.E. Twigg, U.S. Naval Research Laboratory J.A. Freitas, Jr., U.S. Naval Research Laboratory M.A. Mastro, U.S. Naval Research Laboratory J.R. Meyer, U.S. Naval Research Laboratory I. Vurgaftman, U.S. Naval Research Laboratory S. O'Connor, U.S. Naval Research Laboratory N.J. Condon, U.S. Naval Research Laboratory F.J. Kub, U.S. Naval Research Laboratory S.R. Bowman, U.S. Naval Research Laboratory C.R. Eddy, Jr., U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
Gallium nitride is a high quality semiconductor widely used in both optical and electronic devices. The polarity of GaN (+/- c-direction) influences many properties of the resultant material, including chemical reactivity and electric field in these ‘piezoelectric’ materials. Control over the polarity of GaN grown on sapphire and SiC substrates has been previously demonstrated by controlling the growth conditions, doping levels, and buffer or nucleation layer properties. Further, in the case of heavily doped p-type layers, spontaneous polarity inversion has been demonstrated in GaN homoepilayers, switching the doped layer from Ga-polar to N-polar. However, this approach leads to uncontrolled inversion domain boundaries and often results in dopant clustering within the film, impacting film quality and resultant device performance.
In this work we investigate the fabrication of Mg-free inversion layers (ILs) to control the polarity of MOCVD-grown GaN on GaN substrates. By changing the IL material, we demonstrate conversion of GaN polarity in both directions (N-polar to Ga-polar and Ga-polar to N-polar). By employing a patented selective growth method to deposit the IL, the lateral polarity of the GaN can also be alternated, allowing control of the polarity in both vertical and lateral directions. A one-dimensional grating of periodically oriented (PO) GaN stripes was achieved over square-centimeter (or large) areas. The boundaries between polarities are found to be both sharp and vertical, and the growth conditions have been adjusted to result in equal growth rates of both polarities. Chemical etching of the material verifies the polarity of the material. Transmission electron microscopy (TEM) rules out the presence of alternating polar inclusions in the inverted material while showing a strong inversion domain boundary at the vertical interfaces. Dislocation density and grain size are determined through the use of electron channeling contrast imaging. The MOCVD-grown PO GaN structures have been extended in thickness by further HVPE growth. TEM and photoluminescence imaging confirms that the PO GaN structure is maintained throughout the extended growth (up to 80 μm in thickness). This method of GaN polarity inversion offers the promise of engineering both lateral and vertical polarity heterostructures and the potential of novel engineered polarity-based devices.