High-quality N-polar GaN optimization by multi-step temperature growth process

• We report growth optimization of Nitrogen (N)-polar GaN epitaxial layers by hot-wall metal–organic vapor phase epitaxy on 4H-SiC (000) with a misorientation angle of 4° towards the [110] direction. We find that when using a 2-step temperature process for the N-polar GaN growth, step bunching is persistent for a wide range of growth rates (7 nm/min to 49 nm/min) and V/III ratios (251 to 3774). This phenomenon is analyzed in terms of anisotropic step-flow growth and the Ehrlich–Schwöebel barrier, and their effects on the surface step height and step width. The N-polar GaN growth is further optimized by using 3-step and 4-step temperature processes and the layers are compared to those using the 2-step temperature process in terms of surface morphology and defect densities. It is shown that a significantly improved surface morphology with a root mean square of 1.4 nm and with low dislocation densities (screw dislocation density of 2.8 × 108 cm−2 and edge dislocation density of 1.3 × 109 cm−2) can be achieved for 4-step temperature process. The optimized growth conditions allow to overcome the step-bunching problem. The results are further discussed in view of Ga supersaturation and a general growth strategy for high-quality N-polar GaN growth is proposed.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering (hsv//eng)

NATURVETENSKAP  -- Kemi -- Materialkemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Materials Chemistry (hsv//eng)

Nyckelord

N-polar GaN

MOCVD

epitaxial growth

epitaxial III-nitride

surface morphology

2-step temperature process

Ga supersaturation

A1; N-polar GaN; A2; epitaxial III-nitride; A3; surface morphology; B1; MOCVD; B2; 2-step temperature process; C1; Ga supersaturation

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