The improvement of Al2O3/AlGaN/GaN MISHEMT performance by N2 plasma pretreatment

This paper discusses the effect of N 2 plasma treatment before dielectric deposition on the electrical performance of a Al2O3 /AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor(MISHEMT),with Al2O3 deposited by atomic layer deposition.The results indicated that the gate leakage was decreased two orders of magnitude after the Al2O3 /AlGaN interface was pretreated by N 2 plasma.Furthermore,effects of N 2 plasma pretreatment on the electrical properties of the AlGaN/Al2O3 interface were investigated by x-ray photoelectron spectroscopy measurements and the interface quality between Al2O3 and AlGaN film was improved.     

A study on Al2O3 passivation in GaN MOS-HEMT by pulsed stress

This paper studies systematically the drain current collapse in AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors （MOS-HEMTs） by applying pulsed stress to the device. Low-temperature layer of Al2O3 ultrathin film used as both gate dielectric and surface passivation layer was deposited by atomic layer deposition （ALD）. For HEMT, gate turn-on pulses induced large current collapse. However, for MOS-HEMT, no significant current collapse was found in the gate turn-on pulsing mode with different pulse widths, indicating the good passivation effect of ALD Al2O3. A small increase in Id in the drain pulsing mode is due to the relieving of self-heating effect. The comparison of synchronously dynamic pulsed Id - Vds characteristics of HEMT and MOS-HEMT further demonstrated the good passivation effect of ALD Al2O3.     

Removal of GaN film over AlGaN with inductively coupled BCl3/Ar atomic layer etch

Atomic layer etching(ALE)of thin film GaN(0001)is reported in detail using sequential surface modification by BCl₃ adsorption and removal of the modified surface layer by low energy Ar plasma exposure in a reactive ion etching system.The estimated etching rate of GaN is~0.74 nm/cycle.The GaN is removed from the surface of AlGaN after 135 cycles.To study the mechanism of the etching,the detailed characterization and analyses are carried out,including scanning electron microscope(SEM),x-ray photoelectron spectroscopy(XPS),and atomic force microscope(AFM).It is found that in the presence of GaCl_x after surface modification by BCl₃,the GaCl_x disappears after having exposed to low energy Ar plasma,which effectively exhibits the mechanism of atomic layer etch.This technique enables a uniform and reproducible fabrication process for enhancement-mode high electron mobility transistors with a p-GaN gate.     

Simulation and Experimentation for Low Density Drain AlGaN/GaN HEMT

In order to improve the breakdown voltage of AlGaN/GaN high electron mobility transistors （HEMTs）, we report a feasible method of low density drain （LDD） HEMT. The fluoride-based plasma treatment using CF4 gas is performed on the drain-side of the gate edge. The channel two-dimensional electron gas （2DEG） concentrations are modulated by fluoride plasma treatment, and the peak electric field at the gate edge is effectively reduced, so the breakdown voltage is improved. The electric field distributions of the LDD-HEMTs are simulated using the Silvaco software, and the peak of the electric field on the gate edge is effectively reduced. Experimental results show that, compared with the conventional HEMT, LDD-HEMTs have a lower reverse leakage current of the gate, and the breakdown voltage is increased by 36%. The current collapse characteristics of the LDD-HEMTs are confirmed by dual-pulse measurement, and an obvious pulse current reduction is due to the surface states by implanting F ions between the gate and the drain.     

AlGaN/GaN high electron mobility transistor with Al_2O_3+BCB passivation

In this paper, A12O3 ultrathin film used as the surface passivation layer for Al Ga N/Ga N high electron mobility transistor(HEMT) is deposited by thermal atomic layer deposition(ALD), thereby avoiding plasma-induced damage and erosion to the surface. A comparison is made between the surface passivation in this paper and the conventional plasma enhanced chemical vapor deposition(PECVD) Si N passivation. A remarkable reduction of the gate leakage current and a significant increase in small signal radio frequency(RF) performance are achieved after applying Al2O3+BCB passivation.For the Al2O3+BCB passivated device with a 0.7 μm gate, the value of f max reaches up to 100 GHz, but it decreases to 40 GHz for Si N HEMT. The f max/ f t ratio(≥ 4) is also improved after Al2O3+BCB passivation. The capacitance–voltage(C–V) measurement demonstrates that Al2O3+BCB HEMT shows quite less density of trap states(on the order of magnitude of 1010cm-2) than that obtained at commonly studied Si N HEMT.     

AlGaN/GaN MIS-HEMT using NbAlO dielectric layer grown by atomic layer deposition

We present an AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) with an NbAlO high-k dielectric deposited by atomic layer deposition (ALD).Surface morphology of samples are observed by atomic force microscopy (AFM),indicating that the ALD NbAlO has an excellent-property surface.Moreover,the sharp transition from depletion to accumulation in capacitance-voltage (C-V)curse of MIS-HEMT demonstrates the high quality bulk and interface properties of NbAlO on AlGaN.The fabricated MIS-HEMT with a gate length of 0.5 μm exhibits a maximum drain current of 960 mA/mm,and the reverse gate leakage current is almost 3 orders of magnitude lower than that of reference HEMT.Based on the improved direct-current operation,the NbAlO can be considered to be a potential gate oxide comparable to other dielectric insulators.     

Improved performance of AlGaN/GaN HEMT by N2O plasma pre-treatment

The influence of an N_2O plasma pre-treatment technique on characteristics of AlGaN/GaN high electron mobility transistor(HEMT) prepared by using a plasma-enhanced chemical vapor deposition(PECVD) system is presented.After the plasma treatment,the peak transconductance(g_m) increases from 209 mS/mm to 293 mS/mm.Moreover,it is observed that the reverse gate leakage current is lowered by one order of magnitude and the drain current dispersion is improved in the plasma-treated device.From the analysis of frequency-dependent conductance,it can be seen that the trap state density(D_T) and time constant(τ_T) of the N20-treated device are smaller than those of a non-treated device.The results indicate that the N_2O plasma pre-pretreatment before the gate metal deposition could be a promising approach to enhancing the performance of the device.     

Fabricating GeO2passivation layer by N2O plasma oxidation for Ge NMOSFETs application

In this paper, oxidation of Ge surface by N2O plasma is presented and experimentally demonstrated. Results show that1.0-nm GeO2is achieved after 120-s N2O plasma oxidation at 300?C. The GeO2/Ge interface is atomically smooth. The interface state density of Ge surface after N2O plasma passivation is about ～ 3 × 1011cm-2·eV-1. With GeO2passivation,the hysteresis of metal–oxide–semiconductor(MOS) capacitor with Al2O3serving as gate dielectric is reduced to ～ 50 mV,compared with ～ 130 mV of the untreated one. The Fermi-level at GeO2/Ge interface is unpinned, and the surface potential is effectively modulated by the gate voltage.     

Enhancement-mode AlGaN/GaN high electronic mobility transistors with thin barrier

An enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMTs) was fabricated with 15-nm AlGaN barrier layer.E-mode operation was achieved by using fluorine plasma treatment and post-gate rapid thermal annealing.The thin barrier depletion-HEMTs with a threshold voltage typically around-1.7 V,which is higher than that of the 22-nm barrier depletion-mode HEMTs (-3.5 V).Therefore,the thin barrier is emerging as an excellent candidate to realize the enhancement-mode operation.With 0.6-μm gate length,the devices treated by fluorine plasma for 150-W RF power at 150 s exhibited a threshold voltage of 1.3 V.The maximum drain current and maximum transconductance are 300 mA/mm,and 177 mS/mm,respectively.Compared with the 22-nm barrier E-mode devices,V T of the thin barrier HEMTs is much more stable under the gate step-stress.     

Interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor structure by frequency dependent conductance technique

Frequency dependent conductance measurements are implemented to investigate the interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor(MOS) structures. Two types of device structures, namely, the recessed gate structure(RGS) and the normal gate structure(NGS), are studied in the experiment. Interface trap parameters including trap density Dit, trap time constant τit, and trap state energy ETin both devices have been determined. Furthermore,the obtained results demonstrate that the gate recess process can induce extra traps with shallower energy levels at the Al2O3/AlGaN interface due to the damage on the surface of the AlGaN barrier layer resulting from reactive ion etching(RIE).