Growth and polarity control of GaN and AlN on carbon-face SiC by metalorganic vapor phase epitaxy

Abstract

Growth and polarity control of GaN and AlN on carbon-face SiC (C-SiC) by metalorganic vapor phase epitaxy (MOVPE) are reported. The polarities of GaN and AlN layers were found to be strongly dependent on the pre-growth treatment of C-SiC substrates. A pre-flow of trimethyaluminum (TMAl) or a very low NH 3 /TMAl ratio resulted in Al(Ga)-polarity layers on C-SiC. Otherwise, N-polarity layers resulted. The polarities of AlN and GaN layers were conveniently determined by their etching rate in KOH or H 3 PO 4 , namely the etching rate on N-polarity is substantial larger, a method reported earlier. We suggest that the Al adatoms form several Al adlayers on C-SiC and change the incorporation sequence of Ga(Al) and N leading to a metal polarity surface. In addition, the hexagonal pyramids, typical on N-polarity GaN surface, are absent on N-polarity GaN grown on off-axis C-SiC owing to high density of terraces on the substrate surface. The properties of GaN layers grown on C-SiC have been studied by X-ray diffraction and are reported in this paper.

MOVPE growth of nitrogen- and aluminum-polar AlN on 4H-SiC

“…Wet etching is an accurate method for determining III-N layer polarity due to the vastly different etch rates of N-polar and Al-polar surfaces [20,29]. Due to very thin 200 nm layers the Al-polar was only etched for 30 seconds and for N-polar AlN layers the etching time was reduced down to 2 seconds and still the layer was almost completely dissolved ( Figure 3b).…”

“…Due to very thin 200 nm layers the Al-polar was only etched for 30 seconds and for N-polar AlN layers the etching time was reduced down to 2 seconds and still the layer was almost completely dissolved ( Figure 3b). Therefore to lower the etch rate, N-polar samples were additionally etched in 1M 50 • C KOH solution which resulted in a typical N-polar hexagonal pyramids (Figure 3c) which are attributed to being bound by more chemically stable crystalline facets [29,30]. Al-polar AlN layer exhibited typical defect selective etch behavior (Figure 3a) where the hexagonal pits are generated on dislocation cores [18,19].…”

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

“…[11][12][13][14][15] It has been shown that by varying growth temperature, V/III ratio, and surface pretreatment, either N-polar, metal-polar, or a mixed-polarity III-nitride layers can be realized. [16][17][18][19][20][21][22] However, challenges remain for metal organic chemical vapor deposition (MOCVD) growth of N-polar III-nitrides. 11 In particular, polarity inversion domains (IDs) with various shapes are among the most often encountered types of defects in N-polar epitaxial layers and device heterostructures.…”