Tongde Huang

Low-Leakage-Current AlN/GaN MOSHFETs Using

Metal-oxide-semiconductor heterostructure field effect transistors (MOSHFETs) were fabricated with an AlN/GaN heterostructure grown on Si substrates. A 7-nm Al₂O₃ serving as both gate dielectric under the gate electrode and passivation layer in the access region was used. It was found that the Al₂O₃ was superior to SiN_x in increasing the 2-D electron gas (2DEG) density and thereby reducing the access resistance. In addition, the off-state leakage current (<i>I</i>_off) in these AlN/GaN MOSHFETs was reduced by four orders of magnitude to 7.6 × 10^-5 mA/mm as a result of the Al₂ O₃ gate dielectric, compared to that of AlN/GaN HFETs. Meanwhile, the subthreshold slope was improved to a nearly ideal value of 62 mV/dec because of the extremely low <i>I</i>_off. The MOSHFETs with 1-μm gate length exhibited good DC characteristics. A maximum drain current of 745 mA/mm and a peak extrinsic transconductance of 280 mS/mm were achieved.

\hbox{Al}_{2}\hbox{O}_{3}

Monolithic integration of high-performance AlGaN/GaN high-electron mobility transistors (HEMTs) and blue light emitting diodes (LEDs) on sapphire substrates has been demonstrated by metal organic chemical vapor deposition selective growth technique. The integrated HEMT-LED exhibits a peak transconductance (Gm) of 244 mS/mm, a maximum drain current (Id) of 920 mA/mm, and an ON-resistance (Ron) of 2.6 Ω·mm. The forward voltage (VF) of the LED is 3.1 V under an injection current of 10 mA. The integrated LED emits modulated light power efficiently at a wavelength of 470 nm by a serially connected GaN HEMT, showing potential applications such as solid-state lighting, displays, and visible light communications.

for Increased 2DEG

High-performance enhancement-mode (E-mode) AlN/GaN metal-oxide-semiconductor heterojunction field-effect transistors (MOSHFETs) on Si substrates have been demonstrated. Record high peak transconductance G_m of 509 mS/mm and maximum drain current I_d of 860 mA/mm were achieved for E-mode MOSHFETs with a source/drain spacing value L_sd of 0.7 m. Low gate leakage current (<;10^-3 mA/mm) and improved ohmic contact resistance (0.153 Ω·mm) were enabled by a combination of Al₂O₃ gate dielectric and regrown source/drain contacts. Al₂O₃ also significantly increases the 2DEG density under the channel, which is beneficial for device performance by reducing the access resistance. The on-resistance is as low as 1.63 mm. The average regrowth interface resistance across the sample was estimated to be 0.056 Ω·mm. The E-mode MOSHFETs exhibit a high I_on/I_off ratio up to 10⁶.

Monolithic Integration of AlGaN/GaN HEMT on LED by MOCVD

This paper presents the fabrication and characteristics of self-aligned gate-last AlN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs) featuring regrown source/drain for low ON-state resistance (RON). Previously, we demonstrated conventional enhancement-mode AlN/GaN MOSHEMTs on Si substrate with excellent DC performance but limited RF characteristics by large parasitic gate-to-source/drain overlap capacitance. In this paper, the self-aligned gate-last process was developed to minimize the parasitic capacitance. SiNx sidewall and supporting layer were inserted to separate the gate head and source/drain. In the gate-last devices, fT has been improved to be ~40 GHz with a channel length (Lg) of 210 nm. Delay time analysis showed that drain delay was relatively small compared with gate transit and parasitic charging time because of the self-aligned structure.

Enhancement-Mode AlN/GaN MOSHFETs on Si Substrate With Regrown Source/Drain by MOCVD

In this Letter, we report selective epitaxial growth of monolithically integrated GaN-based light emitting diodes (LEDs) with AlGaN/GaN high-electron-mobility transistor (HEMT) drivers. A comparison of two integration schemes, selective epitaxial removal (SER), and selective epitaxial growth (SEG) was made. We found the SER resulted in serious degradation of the underlying LEDs in a HEMT-on-LED structure due to damage of the p-GaN surface. The problem was circumvented using the SEG that avoided plasma etching and minimized device degradation. The integrated HEMT-LEDs by SEG exhibited comparable characteristics as unintegrated devices and emitted modulated blue light by gate biasing.

DC and RF Performance of Gate-Last AlN/GaN MOSHEMTs on Si With Regrown Source/Drain

Enhancement-mode (E-mode) metal-oxide semiconductor high electron mobility transistors (MOSHEMTs) have been fabricated by selective area regrowth technique on AlN/GaN heterostructure. A selectively regrown AlGaN barrier layer could effectively increase the 2-dimensional electron gas (2DEG) density underneath. In comparison with the conventional methods of plasma etching/treatment in the gate region, the regrowth technique can effectively avoid damage caused by the plasma process. Atomic layer deposition of Al2O3 was employed as the gate dielectric. It was found that the Al2O3 on the AlN barrier layer also could induce a higher density of 2DEG. The fabricated E-mode MOSHEMTs with a 1.4-μm gate length exhibited excellent performance of maximum drain current of 530 mA/mm and peak transconductance of 310 mS/mm. The threshold voltage of MOSHEMTs was around +0.2 V. The reverse leakage current was also observed to be around 3.6 × 10-4 mA/mm at Vgs = -1 V and Vds = 6 V. The peak channel electron mobility was extracted to be 880 cm2/Vs using split-CV method. These results indicate that the regrowth technique is a promising method to realize E-mode transistors.

Selective epitaxial growth of monolithically integrated GaN-based light emitting diodes with AlGaN/GaN driving transistors

High-performance AlN/GaN metal-oxide-semiconductor heterojunction field-effect transistors (MOSHEMTs) have been fabricated with source/drain (S/D) regrowth technology by metal-organic chemical vapor deposition (MOCVD). The gate and S/D metallization were produced simultaneously employing Ti/Al/Ni/Au. Low S/D contact resistance of 0.33 Ω·mm and interface resistance less than 0.07 Ω·mm were extracted. The fabricated 550-nm gate-length device exhibits a maximum transcondutance (Gm) of 542 mS/mm and maximum drain current (Id) of 1120 mA/mm with an on/off state current ratio up to 106.

Enhancement-mode AlN/GaN MOSHEMTs fabricated by selective area regrowth of AlGaN barrier layer

Contains table of contents for Part I, table of contents for Section 1, reports on fourteen research projects and a list of publications.