Growth and Properties of Intentionally Carbon‐Doped GaN Layers

Abstract

Carbon-doping of GaN layers with thickness in the mm-range is performed by hydride vapor phase epitaxy. Characterization by optical and electrical measurements reveals semi-insulating behavior with a maximum of specific resistivity of 2 × 10 10 cm at room temperature found for a carbon concentration of 8.8 × 10 18 cm −3 . For higher carbon levels up to 3.5 × 10 19 cm −3 , a slight increase of the conductivity is observed and related to self-compensation and passivation of the acceptor. The acceptor can be identified as C N with an electrical activation energy of 0.94 eV and partial passivation by interstitial hydrogen. In addition, two differently oriented tri-carbon defects, C N -a-C Ga -a-C N and C N -a-C Ga -c-C N , are identified which probably compensate about two-thirds of the carbon which is incorporated in excess of 2 × 10 18 cm −3 .

Current Status of Carbon‐Related Defect Luminescence in GaN

“…[31,33,34,38,39] This is in good agreement with experimental findings of a thermally activated reduction in the resistivity of carbon-doped GaN with an activation energy E A ¼ ð0.95 AE 0.10Þ eV. [40][41][42][43] Furthermore, the acceptor nature of the main defect in carbon-doped bulk GaN was recently verified by the observation of p-type conductivity that was thermally activated with E A ¼ 1.02 eV. [41,44] The calculated acceptor level also agrees with the properties of the commonly observed H1 hole trap at E V þ 0.85-0.90 eV analyzed by deep level transient spectroscopy (DLTS) or minority carrier transient spectroscopy [45][46][47][48][49][50][51][52] and the .…”

“…In particular, the sharp emission onset around 2.6 eV is often obscured by green emission in HVPE-grown GaN. [42,43] Nevertheless, recent improvement of bulk material quality enabled the direct observation of the ZPL in PL measurements. This is shown exemplarily in Figure 4 by data obtained from an undoped bulk GaN sample grown by HVPE.…”

“…To identify the impurities possibly related to certain luminescence bands, concentration series were typically investigated, for carbon doping reported, in previous studies. [41][42][43]61,63,85,87,92,93] The inset shows a zoomed-in spectrum near the ZPL, where even the first phonon replica, denoted by 10, is discernible. Reproduced with permission.…”

“…Further evidence for the need to consider C incorporation in other configurations was given by recent works on highly resistive HVPE-grown GaN. [41][42][43]93] HVPE is inherently carbon-free, resulting in low residual carbon concentrations in nominally undoped HVPE-grown GaN. Accordingly, no YL1 was detected in nominally undoped reference samples.…”

“…In HVPE-grown GaN with intentional carbon doping a strong yellow emission was observed. [42,43,93] Additionally, when the carbon concentration was increased from low 10 17 cm À3 to 1 Â 10 18 cm À3 Zvanut et al observed the emergence of a blue luminescence band around 2.95 eV, which they ascribed to BL C . However, no correlation of YL1 to the carbon concentration was observed.…”