High-k/GaN interface engineering toward AlGaN/GaN MIS-HEMT with improved Vth stability

Abstract

Metal–insulator–semiconductor (MIS) capacitor structures were fabricated on AlGaN/GaN two-dimensional electron gas heterostructure material in order to investigate important aspects of the gate module of a corresponding MIS-high electron mobility transistor device. The process sequence started with an initial wet chemical surface treatment of the as-grown semiconductor material followed by an atomic layer deposition of Al2O3 (high-k first). The electrical analysis focused on the gate leakage current as well as on the shift of the threshold voltage (Vth) upon bias stress in the off- and the on-state regions. The high-k first samples showed much better Vth stability compared to lithographically processed samples, in which the high-k deposition was performed after ohmic contact formation and just before the gate electrode metallization. These results reflect a superior quality of the high-k/GaN interface for the processed structures according to the high-k first approach.

Surface Preconditioning and Postmetallization Anneal Improving Interface Properties and Vth Stability under Positive Gate Bias Stress in AlGaN/GaN MIS‐HEMTs

“…Figure a shows the AFM image of the as‐grown MOCVD GaN‐capped AlGaN/GaN heterostructure surface which shows the typical smooth surface with terraces of mono‐ or bilayer high step edges. [ 10 ] Pits at the step edge terminations which are associated to dislocations are also visible. As comparison, the GaN surface of a sample after ohmic contacts patterning, organic wet cleaning and subsequent annealing is shown in Figure 2b.…”

“…The V th instability under different bias conditions in AlGaN/GaN-based MIS-HEMTs has been often reported. [9][10][11][12][13] In particular, serious V th shift induced by forward gate bias stress due to electron trapping at the dielectric/ III-N interface is one of the major concern in terms of device reliability. [14][15][16][17] Therefore, the minimization of trap states at the interface is a critical issue for GaN-based MIS-HEMTs.…”

“…In this context, this work investigates the interface of Al 2 O 3 /III-nitrides structures where atomic layer deposited (ALD) Al 2 O 3 is used because of its promising properties as gate dielectric in MIS-HEMTs in terms of large bandgap (7-9 eV), high dielectric constant (8)(9)(10), and large conduction-band offset to GaN (%2.1 eV). [25,26] In particular, the effects on the Al 2 O 3 /III-nitrides interface of an O 2 plasma-based surface treatment applied before the Al 2 O 3 deposition and of a N 2 annealing after gate metallization are investigated.…”

“…Frequency dispersion in forward bias region of the C-V characteristics of Al 2 O 3 /GaN/AlGaN/GaN diodes having 16 nm-thick Al 2 O 3 without treatment applied (black rectangle), after SPC (blue circle), and SPC combined with PMA (green triangle). The frequency ranges from 1 kHz to 1 MHz, e.g.,[1,3,10,30, 100, 300, 1000 kHz].…”

Material investigations for improving stability of Au free Ta/Al-based ohmic contacts annealed at low temperature for AlGaN/GaN heterostructures

“…Ohmic contacts could be processed after the gate module in case the gate can withstand the reduced temperatures but degrades with temperatures above 700 • C e.g. by crystallization of an amorphous dielectric [20].…”