PC-Fri-5 - Impact of Dislocations on Leakage Currents of GaN-on-GaN pn-Diodes: A Statistical Approach Comparing X-Ray Topography with Electrical Characteristics

2. Physics and characterization
Roland Weingärtner¹ , Leon Schiller¹, Alexander Kinstler², Richard Neumann², Frank Brunner³, Eldad Bahat Treidel³, Enrico Brusaterra³, Matthias Marx⁴, Sven Besendörfer^1
1 Fraunhofer Institute for Integrated Systems and Device Technology IISB, Schottkystr. 10, Erlangen, Germany
² Infineon Technologies AG, Am Campeon 1-15, 85579 Neubiberg, Germany
³ Ferdinand-Braun-Institut gGmbH (FBH), Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
⁴ AIXTRON SE, Dornkaulstraße 2, 52134 Herzogenrath, Germany

Abstract text
The wide-bandgap semiconductor gallium nitride (GaN) draws increasingly industrial attention for power electronic applications. However, performance of devices based on heteroepitaxy suffers from the high defect densities of the epilayer. In addition, thick layers for vertical device structures which support high voltage are difficult to obtain with low bow. Therefore, GaN-on-GaN based device technology is a desired approach.

Typically, the relation between material defects such as dislocations and device performance are investigated on a small, microscopic scale or on heteroepitaxial based devices [1, 2]. In this framework we investigate the impact of dislocations in the GaN substrate and consequently the epilayer on diode performance on full wafer scale. On five HVPE-grown 2”-GaN substrates we fabricated 552 vertical pn-diodes each with effective areas of 3.0, 6.0 and 12.0 × 10^-4 cm^-2 in checkerboard pattern throughout the wafer. The leakage current of the pn-diodes is highly sensitive to either point defects or dislocation content while fluctuations in technological process steps have little influence. It is the aim of this work to differentiate between these effects by a large statistical approach. X-ray topography is used to characterize the substrate with epilayer and the wafer with devices on top using Cu:0004 reflection. Macro-defects like wafer preparation damages and V-pits can be identified under the diodes’ active areas in the topographs and directly correlated to their IV-characteristics. We show that X-ray topography not only reveals dislocation networks in the epilayer, but also that diffraction intensity is correlated to the dislocation density and thus influences the leakage current of the diode. The latter effect is investigated at high blocking voltages at -700V where still most diodes don´t show electrical breakdown.

Conclusively, we show that besides of technological processing impact on the leakage current, also the dislocation network of the epilayer must be considered to understand the reverse bias characteristics and should be considered in device processing.

[1] Besendörfer, et. al. (2020), Sci. Reports 10 17252.

[2] Brunner, et al., physica status solidi (RRL) – Rapid Research Letters, vol. 18, no. 11, Nov. 2024, doi: 10.1002/pssr.202400013.