Experimental characterization of impact ionization coefficients for electrons and holes in GaN grown on bulk GaN substrates

Abstract

Epitaxial p-i-n structures grown on native GaN substrates have been fabricated and used to extract the impact ionization coefficients in GaN. The photomultiplication method has been used to experimentally determine the impact ionization coefficients; avalanche dominated breakdown is confirmed by variable-temperature breakdown measurements. To facilitate photomultiplication measurements of both electrons and holes, the structures include a thin pseudomorphic In0.07Ga0.93N layer on the cathode side of the drift layer. Illumination with 193 nm and 390 nm UV light has been performed on diodes with different intrinsic layer thicknesses. From the measured multiplication characteristics, the impact ionization coefficients of electrons (α) and holes (β) were determined for GaN over the electric field range from 2 MV/cm to 3.7 MV/cm. The results show that for transport along the c-axis, holes dominate the impact ionization process at lower electric field strengths; the impact ionization coefficient of electrons becomes comparable to that of holes (β/α<5) for electric field strengths above 3.3 MV/cm.

Avalanche Multiplication Noise in GaN p–n Junctions Grown on Native GaN Substrates

“…As the reverse bias increases, the barrier flattens out and the photocurrent increases. When the reverse bias increases further, the multiplication process starts and both the photocurrent and dark current increase sharply . The inset of Figure a shows the multiplication gain M for pure hole injection.…”

“…Edge termination with N‐ion implantation was used to suppress edge effects. The fabrication process details have been reported in the study by Cao et al…”

“…Detailed impact ionization data in low defect density GaN is needed for device design and applications. Previous reports of the impact ionization coefficients for electrons and holes in GaN p–n junctions grown on single‐crystal bulk GaN substrates showed significant asymmetry between the coefficients for electrons and holes . In applications, this asymmetry can significantly impact the excess noise in avalanche photodiodes (APDs) and the performance of impact ionization avalanche transit time diodes (IMPATTs) …”

“…The excess noise characteristics of the GaN p–n diodes for pure hole injection using 390 nm UV light are also reported. In addition, the ratio of the impact ionization coefficients ( α / β ) is obtained from multiplication noise measurements and compared with results obtained from photocurrent‐method extraction of the impact ionization coefficients …”

Device processing and junction formation needs for ultra-high power Ga2O3 electronics

“…To date, only a limited number of dielectrics have been used a gate overlap field plates and the optimization of material and geometry is largely unexplored. [61][62][63][64][65] To understand the breakdown characteristics of a power device, it is also important to know the impact ionization coefficients of electrons and holes as a function of the electric field in the semiconductor. [61] There are, as yet, no experimental measurements of these quantities for Ga 2 O 3 .…”