Yu-Lin Hsiao

Growth of GaN film on 150mm Si (111) using multilayer AlN∕AlGaN buffer by metal-organic vapor phase epitaxy method

High quality GaN film was successfully grown on 150mm Si (111) substrate by metal-organic vapor phase epitaxy method using AlN multilayer combined with graded AlGaN layer as buffer. The buffer layer structure, film quality, and film thickness are critical for the growth of the crack-free GaN film on Si (111) substrate. Using multilayer AlN films grown at different temperatures combined with graded Al1−xGaxN film as the buffer, the tensile stress on the buffer layer was reduced and the compressive stress on the GaN film was increased. As a result, high quality 0.5μm crack-free GaN epitaxial layer was successfully grown on 6in. Si substrate.

460-nm InGaN-Based LEDs Grown on Fully Inclined Hemisphere-Shape-Patterned Sapphire Substrate With Submicrometer Spacing

This letter investigates 460-nm InGaN-based light-emitting diodes (LEDs) grown on a hemisphere-shape- patterned sapphire substrate (HPSS) with submicrometer spacing. The full-width at half-maximum of the (102) plane rocking curves for GaN layer grown on a conventional sapphire substrate (CSS) and HPSS are 480 and 262 arcsec, respectively. Such improvement is due to the reduction of the pure edge threading dislocations. At the forward current of 20 mA, the light output power of the LEDs grown on CSS and HPSS were 4.05 and 5.86 mW, respectively. This improvement of 44% light-output power can be attributed to the improved quality of the material and the increase of the light extraction by the fully inclined facets of the HPSS.

Effects of AlxGa1−xN interlayer for GaN epilayer grown on Si substrate by metal-organic chemical-vapor deposition

GaN film grown on Si substrate using multilayer AlN/AlxGa1−xN buffer is studied by the low-pressure metal-organic chemical-vapor deposition method. The AlxGa1−xN films with Al composition varying from 1 to 0.66 were used to accommodate the stress induced between GaN and the Si substrate during GaN growth. The correlation of the Al composition in the AlxGa1−xN films with respect to the stress induced in the GaN film grown was studied using high-resolution x-ray diffraction, including symmetrical and asymmetrical ω/2θ scans and reciprocal space maps. It is found that with proper design of the Al composition in the AlxGa1−xN buffer layer, crack-free GaN film can be successfully grown on 6 in. Si (111) substrates using multilayer AlN and AlxGa1−xN buffer layers.

Performance Improvements of AlGaN/GaN HEMTs by Strain Modification and Unintentional Carbon Incorporation

An advanced AlGaN/GaN HEMT structure, grown on a sapphire substrate by MOCVD utilizing a high temperature (HT) AlN interlayer (IL) and a multilayer high-low-high temperature (HLH) AlN buffer layer, demonstrates a superior performance both in breakdown voltage (>200 V) and maximum drain current (IDSS = 667 mA/mm). The HT AlN IL produces an additional compressive strain into the above GaN layer. Accordingly, an AlGaN barrier, grown on the more compressive GaN, introduces less tensile strain leading to an improvement in surface morphology (RMS = 0.19 nm in 2 × 2 μm2), a remarkable increase in 2DEG mobility by 46% (μs = 1900 cm2/Vs) and a decrease in densities of defects acting as paths for the leakage current through the AlGaN barrier. A high semi-insulating buffer is achieved by eliminating leakage paths both through the buffer layer and the buffer-substrate interfacial layer. These result from an increase in unintentional carbon introduced by AlN layers, especially by a low temperature AlN layer; which are grown under low pressure (50 Torr). Lastly, the decrease in AlGaN barrier tensile strain and low leakage current in the advanced HEMTs structure using an HT AlN IL and an HLH AlN buffer are promising for an improvement in AlGaN/GaN HEMTs’ reliability.

Material growth and device characterization of AlGaN/GaN single-heterostructure and AlGaN/GaN/AlGaN double-heterostructure field effect transistors on Si substrates

An Al0.2Ga0.8N/GaN/Al0.1Ga0.9N double-heterostructure field effect transistor (DH-FET) structure was grown on a 150-mm-diameter Si substrate and the crystalline quality of the epitaxial material was found to be comparable to that of an Al0.2Ga0.8N/GaN single-heterostructure field effect transistor (SH-FET) structure. The fabricated DH-FET shows a lower buffer leakage current of 9.2 × 10−5 mA/mm and an improved off-state breakdown voltage of higher than 200 V, whereas the SH-FET shows a much higher buffer leakage current of 6.0 × 10−3 mA/mm and a lower breakdown voltage of 130 V. These significant improvements show that the Al0.2Ga0.8N/GaN/Al0.1Ga0.9N DH-FET is an effective structure for high-power electronic applications.

Investigation of the low-temperature AlGaN interlayer in AlGaN/GaN/AlGaN double heterostructure on Si substrate

A low-temperature (LT) AlGaN interlayer is inserted in the Al0.1Ga0.9N back barrier layer of an Al0.2Ga0.8N/GaN/Al0.1Ga0.9N double heterostructure grown on a 150 mm Si substrate. It is found that the 21-nm-thick LT-AlGaN interlayer plays an important role in stress relaxation and dislocation reduction of the Al0.1Ga0.9N back barrier layer, especially for screw dislocation reduction. In addition, a buffer breakdown voltage higher than 600 V is achieved, which is much higher than those of conventional heterostructures. These results demonstrate the effectiveness of combining the LT-AlGaN interlayer and the Al0.2Ga0.8N/GaN/Al0.1Ga0.9N double heterostructure on a Si substrate to increase the breakdown voltage for high-power applications.

Investigation of the inserted LT-AlGaN interlayer in AlGaN/GaN/AlGaN DH-FET strucutre on Si substrates

A novel AlGaN/GaN/AlGaN double-heterostructure field effect transistor (DH-FET) structure with an inserted LT-AlGaN interlayer grown on 150 mm Si substrate has been studied. The DH-FET structure has been characterized by transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS) and X-ray diffraction (XRD). It is found that the inserted LT-AlGaN interlayer can further induce the compressive stress to compensate the tensile stress. Furthermore, the inserted LT-AlGaN interlayer acts as a dislocation filter to reduce threading dislocation propagation. These results indicate that the inserted LT-AlGaN interlayer plays an important role in the novel DH-FET structure.

DC and RF Performance Improvement of 70 nm Quantum Well Field Effect Transistor by Narrowing Source–Drain Spacing Technology

A 70 nm InAs channel quantum well field effect transistor (QWFET) fabricated by a narrowing source–drain (S/D) spacing technique was realized for future high-speed and logic applications. The S/D spacing was decreased from 3 to 0.65 µm through a simple fabrication process, which is an ameliorative redeposition ohmic technique. The drain-source current density and transconductance of the device were increased from 391 to 517 mA/mm and from 946 to 1348 mS/mm after the scaling of the S/D spacing, respectively. In addition, the current gain cutoff frequency ( fT) was also increased from 185 to 205 GHz. These results show that the easy method can effectively improve the III–V QWFET device performance for high-frequency and high-speed applications.

An AlGaAs/InGaAs HEMT Grown on Si Substrate with Ge/GexSi1-x Metamorphic Buffer Layers

An AlGaAs/InGaAs HEMT grown on Si substrate with Ge/Ge x Si 1−x buffer is demonstrated. The Ge/Ge x Si 1−x metamorphic buffer layer used in this structure was only 1.0 μgm thick. The electron mobility in the In 0.18 Ga 0.82 As channel of the HEMT sample was 3,550 cm 2 /Vs. After fabrication, the HEMT device demonstrated a saturation current of 150 mA/mm and a maximum transconductance of 155 mS/mm. The well behaved characteristics of the HEMT device on the Si substrate are believed to be due to the very thin buffer layer achieved and the lack of the antiphase boundaries (APBs) formation and Ge diffusion into the GaAs layers.