Overview of carrier compensation in GaN layers grown by MOVPE: toward the application of vertical power devices

Abstract

Sources of carrier compensation in n-type and p-type GaN layers grown by metalorganic vapor phase epitaxy were quantitatively identified by a combination of Hall-effect analysis and deep level transient spectroscopy. For n-type GaN, we identified three electron compensation sources: residual carbon atoms likely sitting on nitrogen sites (CN), an electron trap at the energy level of EC –0.6 eV (the E3 trap), and self-compensation appearing with increasing donor concentration. We showed that the CN also play a key role in hole compensation in p-type GaN by forming donor-like charged states. We also investigated the reduction of acceptor concentrations (Na) in highly Mg-doped GaN. Atomic-resolution scanning transmission electron microscopy revealed that electrically inactive Mg atoms of 3/2 atomic layers are segregated at the boundary of pyramidal inversion domains. The Na reduction can be explained by this Mg segregation.

A Deep Carbon‐Related Acceptor Identified through Photo‐Induced Electron Paramagnetic Resonance

“…The C N (0/+) level is also thought to be identified by PL in HVPE GaN . Electrical measurement such as deep‐level transient spectroscopy (DLTS) provides more definitive understanding, and a variety of levels have been associated with carbon, including those for a deep acceptor, deep donor, and shallow donor . To date, most studies are performed on thin films with a limited range of carbon doping.…”

“…The positive contribution of carbon to grow semi‐insulating material contrasts the possible negative aspects that arise when trying to achieve lightly p‐doped layers. Here, the carbon that is unintentionally incorporated during growth is thought to capture holes created by the p‐type dopant . Several theoretical studies have addressed the cause of carbon's “dual nature.” Many show that carbon substituting for nitrogen (C N ) is a deep acceptor with a defect level C N (−/0) 0.90 eV above the valence band edge, and therefore is useful in the production of semi‐insulating GaN .…”

“…However, several groups also predict a second level, C N (0/+) which, if the Fermi level is low enough, could cause hole capture . Such is thought to be the situation in the lightly p‐doped GaN films …”

1.2-kV Vertical GaN Fin-JFETs: High-Temperature Characteristics and Avalanche Capability

“…A 0.57 eV trap level is obtained at the zero E avg intercept [see Fig. 7(d)], implying that the dominant trap for the PF transport is likely the E C −0.6 eV electron trap widely reported in the GaN epitaxial layers on GaN substrates grown by the metal-organic chemical vapor deposition (MOCVD) [34]- [36], which may originate from the residual carbon atoms [34], point defects [35], or nitrogen antisites [36].…”

Metalorganic Chemical Vapor Deposition Gallium Nitride with Fast Growth Rate for Vertical Power Device Applications

“…A recent paper systematically reviewed the compensation effect in GaN. [ 16 ] In that work, three primary compensation mechanisms were reported: 1) compensation through carbon on nitrogen site ( C N ) acceptor states; 2) auto‐compensation due to amphoterism by C (i.e., C N acceptors and carbon on gallium site ( C Ga ) donors) at high carbon doping concentrations; and 3) compensation through the often reported E C ‐0.60 eV trap that has been affiliated with iron on gallium site (Fe Ga ). [ 17,18 ] Although Fe was identified as a common impurity in MOCVD GaN, [ 17–19 ] it can be significantly suppressed via optimized wafer cleaning, susceptor selection, and controlled growth condition.…”