A study on Al_2O_3 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.

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

In this paper, Al2O3 ultrathin film used as the surface passivation layer for A1GaN/GaN 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） SiN 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 0.7μm gate, the value of fmax reaches up to 100 GHz, but it decreases to 40 GHz for SiN HEMT. The fmax/ft ratio （〉 4） is also improved after Al2O3＋BCB passivation. The capacitancevoltage （C-V） measurement demonstrates that Al2O3＋BCB HEMT shows quite less density of trap states （on the order of magnitude of 1010 cm-2） than that obtained at commonly studied SiN HEMT.

Comparative study on characteristics of Si-based AlGaN/GaN recessed MIS-HEMTs with HfO2 and Al2O3 gate insulators

Two types of enhancement-mode(E-mode)AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors(MIS-HEMTs)with different gate insulators are fabricated on Si substrates.The HfO2 gate insulator and the Al2O3 gate insulator each with a thickness of 30 nm are grown by the plasma-enhanced atomic layer deposition(PEALD).The energy band diagrams of two types of dielectric MIS-HEMTs are compared.The breakdown voltage(VBR)of HfO2 dielectric layer and Al2O3 dielectric layer are 9.4 V and 15.9 V,respectively.With the same barrier thickness,the transconductance of MIS-HEMT with HfO2 is larger.The threshold voltage(Vth)of the HfO2 and Al2O3 MIS-HEMT are 2.0 V and 2.4 V,respectively,when the barrier layer thickness is 0 nm.The C-V characteristics are in good agreement with the Vth's transfer characteristics.As the barrier layer becomes thinner,the drain current density decreases sharply.Due to the dielectric/AlGaN interface is very close to the channel,the scattering of interface states will lead the electron mobility to decrease.The current collapse and the Ron of Al2O3 MIS-HEMT are smaller at the maximum gate voltage.As Al2O3 has excellent thermal stability and chemical stability,the interface state density of Al2O3/AlGaN is less than that of HfO2/AlGaN.

Enhancement in Light Extraction Efficiency of GaN-Based Light-Emitting Diodes Using Double Dielectric Surface Passivation

SiO2Al2O3 double dielectric stack layer was deposited on the surface of the GaN-based light-emitting diode (LED). The double dielectric stack layer enhances both the electrical characteristics and the optical output power of the LED because the first Al2O3 layer plays a role of effectively passivating the p-GaN surface and the second lower index SiO2 layer increases the critical angle of the light emitted from the LED surface. In addition, the effect of the Fresnel reflection is also responsible for the enhancement in output power of the double dielectric passivated LED. The leakage current of the LED passivated with Al2O3 layer was -3.46 × 10-11 A at -5 V, at least two and three orders lower in magnitude compared to that passivated with SiO2 layer (-7.14 × 10-9 A) and that of non-passivated LED (-1.9 × 10-8 A), respectively, which indicates that the Al2O3 layer is very effective in passivating the exposed GaN surface after dry etch and hence reduces nonradiative recombination as well as reabsorption of the emitted light near the etched surface.

超薄Al_2O_3绝缘栅AlGaN/GaN MOS-HEMT器件研究

采用原子层淀积(ALD),实现超薄(3.5nm)Al2O3为栅介质的高性能AlGaN/GaN金属氧化物半导体高电子迁移率晶体管(MOS-HEMT).新型AlGaN/GaN MOS-HEMT器件栅长0.8μm,栅宽60μm,栅压为+3.0V时最大饱和输出电流达到800mA/mm,最大跨导达到150ms/mm,与同样尺寸的AlGaN/GaNHEMT器件相比,栅泄漏电流比MES结构的HEMT降低两个数量级,开启电压保持在?5.0V.C-V测量表明Al2O3能够与AlGaN形成高质量的Al2O3/AlGaN界面.

Surface Leakage Currents in SiN and Al_2O_3 Passivated AlGaN/GaN High Electron Mobility Transistors

Surface leakage currents of A1GaN/GaN high electron mobility transistors are investigated by utilizing a circular double-gate structure to eliminate the influence of mesa leakage current. Different mechanisms are found under various passivation conditions. The mechanism of the surface leakage current with AI2 03 passivation follows the two-dimensional variable range hopping model, while the mechanism of the surface leakage current with SiN passivation follows the Frenkel-Poole trap assisted emission. Two trap levels are found in the trap-assisted emission. One trap level has a barrier height of 0.22eV for the high electric field, and the other trap level has a barrier height of 0.12eV for the low electric field.

Excellent-Performance AlGaN/GaN Fin-MOSHEMTs with Self-Aligned Al_2O_3Gate Dielectric

A1GaN/GaN fin-shaped metal-oxide-semiconductor high-electron-mobility transistors （fin-MOSHEMTs） with dif- ferent fin widths （30Ohm and lOOnm） on sapphire substrates are fabricated and characterized. High-quality self-Migned Al2O3 gate dielectric underneath an 80-nm T-shaped gate is employed by Muminum self-oxidation, which induces 4 orders of magnitude reduction in the gate leakage current. Compared with conventional planar MOSHEMTs, short channel effects of the fabricated fin-MOSHEMTs are significantly suppressed due to the tri- gate structure, and excellent de characteristics are obtained, such as extremely fiat output curves, smaller drain induced barrier lower, smaller subthreshold swing, more positive threshold voltage, higher transconductance and higher breakdown voltage.

Al_2O_3/AlGaN/GaN MOSH结构的制备和性能研究

采用激光脉冲沉积法(PLD)在AlGaN/GaN半导体异质结构衬底上沉积Al2O3栅介质层,并对该异质结构的电学性能进行研究。结果表明,Al2O3栅介质层改善了异质结构的界面质量,增强了器件结构的抗击穿电场强度。研究了沉积氧分压对异质结构性能的影响,电流-电压(I-V)测试结果表明,适当氧分压(0.1 Pa)有利于降低栅漏电流。Hall测量和电容-电压(C-V)模拟结果表明,不同的氧分压会改变Al2O3/AlGaN界面处的正电荷密度,从而改变半导体内的二维电子气(2DEG)密度。

The improvement of Al_2O_3 /AlGaN/GaN MISHEMT performance by N_2 plasma pretreatment

This paper discusses the effect of N2 plasma treatment before dielectric deposition on the electrical performance of a Al203/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor （MISHEMT）,with Al203 deposited by atomic layer deposition.The results indicated that the gate leakage was decreased two orders of magnitude after the Al203/AlGaN interface was pretreated by N2 plasma.Furthermore,effects of N2 plasma pretreatrnent on the electrical properties of the AlGaN/Al2O3 interface were investigated by x-ray photoelectron spectroscopy measurements and the interface quality between Al203 and AlGaN film was improved.

Interface states in Al_2O_3/AlGaN/GaN metal-oxide-semiconductor structure by frequency dependent conductance technique

Frequency dependent conductance measurements are implemented to investigate the interface states in Al2O3/A1GaN/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 includ-ing trap density Dit, trap time constant ιit, and trap state energy ET in 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）.

Al2O3绝缘层的AlGaN/GaN MOSHEMT器件研究

在研制AlGaN/GaNHEMT器件的基础上,采用ALD法制备了Al2O3AlGaN/GaNMOSHEMT器件.通过X射线光电子能谱测试表明在AlGaN/GaN异质结材料上成功淀积了Al2O3薄膜.根据对HEMT和MOSHEMT器件肖特基电容、器件输出以及转移特性的测试进行分析发现:所制备的Al2O3薄膜与AlGaN外延层间界面态密度较小,因而MOSHEMT器件呈现出较好的栅控性能;其次,该器件的栅压可以加至+3V,此时的最大饱和电流达到800mA/mm,远远高于肖特基栅HEMT器件的最大输出电流;而且栅漏反偏状态下的泄漏电流却减小了两个数量级,提高了器件的击穿电压,通过进一步分析认为泄漏电流主要来源于Fowler-Nordheim隧穿.

Study of GaN MOS-HEMT using ultrathin Al_2O_3 dielectric grown by atomic layer deposition

We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic-layer deposited (ALD) Al2O3 as the gate dielectric. Through further decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process,a device with maximum transconductance of 150 mS/mm was produced. The drain current of this 0.8 μm gate-length MOS-HEMT could reach 800 mA/mm at +3.0 V gate bias. Compared to a conventional AlGaN/GaN HEMT of similar design,better interface property,lower leakage current,and smaller capacitance-voltage (C-V) hysteresis were obtained,and the superiority of this MOS-HEMT device structure with ALD Al2O3 gate dielectric was exhibited.