On the polarity determination and polarity inversion in nitrogen-polar group III-nitride layers grown on SiC

Abstract

Note: This paper is part of the Special Topic on Wide Bandgap Semiconductor Materials and Devices.

Polarity Control by Inversion Domain Suppression in N-Polar III-Nitride Heterostructures

“…Furthermore, it is essential to point out that for both the initial AlN layers are dominantly N-polar. This is the key point why LT AlN NLs can be completely etched away at the macroscale using KOH . The observed IDBs are similar to the Al 9 O 3 N 7 structures reported by Asaka et al and Stolyarchuk et al We also note that a simple cross-section overlap of adjacent N-polar and Al-polar lattices will result in the same appeared structure (see Figure S2 in the Supporting Information for comparisons of simulated ADF STEM images of different lattice overlap scenarios).…”

“…Furthermore, HR-XRD measurements combined with KOH etching indicate that the LT and HT AlN NLs are all N-polar on a macroscale, as evidenced by the disappearance of the AlN 0002 peak upon KOH etching (additional information on polarity determination of samples before and after KOH etching from HR-XRD can be found in the Supporting Information ). Recently, we have shown that KOH etching may provide an inconclusive polarity assignment in the case of mix-polarity AlN as Al-polar domains may be under- or overetched through adjacent N-polar pyramid domains and thus may remain undetected . Therefore, cross-sectional atomically resolved ADF STEM is used to determine the polarity by following the stacking order of Al and N atom positions along the growth direction.…”

“…Nitrogen-rich growth conditions with a high V/III ratio were claimed to be required to realize N-polar III-nitride layers. , Furthermore, a distinct unintentional impurity incorporation of oxygen, carbon, and hydrogen in N-polar GaN layers was reported . In our recent study, a three-dimensional (3D) growth mode of N-polar AlN NLs on SiC (0001̅) was identified as the likely cause for the observed polarity inversion . We suggested that the ⟨40–41⟩ facets of the 3D islands facilitate enhanced unintentional incorporation of oxygen, which leads to the formation of inclined inversion domain boundaries (IDBs) .…”

“…In our recent study, a three-dimensional (3D) growth mode of N-polar AlN NLs on SiC (0001̅) was identified as the likely cause for the observed polarity inversion . We suggested that the ⟨40–41⟩ facets of the 3D islands facilitate enhanced unintentional incorporation of oxygen, which leads to the formation of inclined inversion domain boundaries (IDBs) . On the other hand, intentional doping was also found to influence the polarity.…”

“…Nitrogen-polar (N-polar) HEMTs exhibit unique characteristics compared with metal-polar devices, − such as the feasibility to fabricate ohmic contact with low resistivity, an enhanced carrier confinement with a natural back barrier, as well as improved device scalability . However, growth of N-polar group III-nitrides is not trivial because of unintended formation of polarity inversion domains (IDs). − Notably, the identification of polarity may be challenging with some limitations of commonly used techniques …”