Abstract
We applied Kelvin probe force microscopy (KPFM) to characterize the p-n junction grown on hydride vapor-phase epitaxy GaN wafers with three different doses of the p-type dopant Mg. The distributions of the contact potential difference (CPD) were visualized to observe the abrupt changes in the CPD across the p-n junction. Based on this result, we attempted to evaluate the electrostatic potential distributions across the GaN p-n junction, which consequently provide the dopant concentrations in the p-type region (NA) and unintentionally doped regions (NUID). The obtained values of NA in this study were two orders of magnitude smaller than doped Mg concentrations, while those of NUID were consistent with the results of secondary ion mass spectroscopy. We demonstrate the potential of KPFM in the evaluation of GaN p-n junctions.
Highlights
Gallium nitride (GaN) power devices have not yet achieved their full potential in performance because of the challenge to obtain low-resistance p-type GaN (p-GaN), which is needed for power saving and an ohmic contact on the p-type region
FIG. 2. [(a)–(c)] atomic force microscopy (AFM) topographic images and [(d)–(f)] corresponding Kelvin probe force microscopy (KPFM)-contact potential differences (CPDs) images across the p-n junction of GaN and [(g)–(i)] CPD line profiles averaged in the blue rectangles marked in the CPD images [in (d)–(f)] and theoretical potentials expressed by Eqs. (1)–(3)
The ΔCPD did not match the Vbi, the CPD profiles are rather effective in estimating the width of the depletion regions in the p-n junction because the CPD profile should be specific to the potential feature in the sample, even though it is detected through the surface band bending layer
Summary
Gallium nitride (GaN) has attracted much attention as a material for generation semiconductor power devices owing to its attractive properties, such as a large band gap (3.4 eV), a high breakdown voltage (∼3.5 MV/cm), and a high saturation velocity (∼2.5 × 107 cm/s).1–3 Because these properties are suitable for high power and rapid switching devices, investigations for practical devices, such as metal–oxide–semiconductor field-effect transistors, have been conducted.4–7 GaN power devices have not yet achieved their full potential in performance because of the challenge to obtain low-resistance p-type GaN (p-GaN), which is needed for power saving and an ohmic contact on the p-type region. GaN nanowires.20,21 Here, we apply KPFM to a cleaved m-plane surface of GaN p-n junctions with different Mg concentrations.
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