Reduction of reverse-bias leakage current in Schottky diodes on GaN grown by molecular-beam epitaxy using surface modification with an atomic force microscope

Abstract

The characteristics of dislocation-related leakage current paths in an AlGaN/GaN heterostructure grown by molecular-beam epitaxy and their mitigation by local surface modification have been investigated using conductive atomic force microscopy. When a voltage is applied between the tip in an atomic force microscope ͑AFM͒ and the sample, a thin insulating layer is formed in the vicinity of the leakage paths where current is observed. As the insulating layer reaches a thickness of 2-3 nm, the leakage current is blocked and subsequent growth of the layer is prevented. Although conductive screw or mixed dislocations are observed, dislocations with a screw component that do not conduct current are also apparent. The reverse-bias leakage current is reduced by a factor of two in a large-area diode fabricated on an area modified in this manner with an AFM compared to typical diodes fabricated on unmodified areas with comparable series resistances, confirming that dislocation-related leakage current paths are a major component of the reverse-bias leakage current in Schottky diodes fabricated on nitride material.

Reverse-bias leakage current reduction in GaN Schottky diodes by electrochemical surface treatment

“…The procedure used to perform CAFM is described elsewhere. 3 The measured tip-sample currents for the unmodified and modified surfaces are shown in Figs. 2͑a͒ and 2͑b͒, respectively.…”

“…2 Previous studies have shown that these leakage paths can be blocked by the formation of insulating layers over these leakage paths using an atomic force microscope ͑AFM͒. 3 Because this process is not practical as a large-scale surface treatment due to the time-intensive nature of the AFM surface modification procedure, an alternative technique suitable for efficient treatment of large surfaces would be desirable.…”

“…This process should attract OH Ϫ ions which are present in high concentrations in the solution to the GaN surface, similar to the AFM surface modification process in which the positive sample bias attracts ions from the thin water layer typically present on the surface as the tip passes over leakage paths. 3 Ohmic contacts employing Ti/Al/Ti/Au metallization 7 annealed at 750°C for 30 s were fabricated on the sample surface prior to surface treatment to decrease the resistance between the cathode contact wire and the sample. Schottky contacts consisting of 1200 Å Ni were fabricated on the modified and unmodified surfaces.…”

Nanoscale Characterization of Electronic and Electrical Properties of III-Nitrides by Scanning Probe Microscopy

“…Miller et al [41] also observed dislocation-related leakage paths in AIGaN/GaN heterostructures. In addition, they demonstrated that the process of scanning with a voltage applied between the tip and sample can lead to the formation of an insulating layer (of gallium oxide) [42] over the dislocation.…”

“…They employed scanning capacitance microscopy (SCM) to investigate threading dislocations in GaN. Since then, SCM [13][14][15], electrostatic force microscopy (EFM) [16][17][18][19][20], Kelvin probe force microscopy (KPFM) [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36],conductive-tip atomic force microscopy (C-AFM) [35][36][37][38][39][40][41][42][43][44][45][46], piezoresponse force microscopy (PFM) [47][48][49][50] and scanning gate microscopy (SGM) [51] have all been employed to characterize III-nitride films and surfaces.…”