High quality AlN with uniform in-plane strain on nano-patterned AlN templates achieved by preset strain modulation

High-quality AlN with uniform in-plane strain has been attempted with preset strain modulation on nano-patterned AlN templates (NPATs). It is found that this strain preset frame can effectively improve both the tilt and twist features of AlN on NPATs, further greatly decreasing threading dislocation density. More importantly, the AlN epilayer after completing coalescence can maintain the in-plane uniform compressive strain. Adopting AlN templates achieved in this scheme, the chip-on-wafer light output power (LOP) of AlGaN light-emitting diode (LED) reaches 10.2 mW at 100 mA with single emission peak at 280 nm, which increases by 22.3% than the LOP of LED device without adopting this strain preset frame.

Monolithic Integration of Nano-Ridge Engineered InGaP/GaAs HBTs on 300 mm Si Substrate

Nano-ridge engineering (NRE) is a novel method to monolithically integrate III–V devices on a 300 mm Si platform. In this work, NRE is applied to InGaP/GaAs heterojunction bipolar transistors (HBTs), enabling hybrid III-V/CMOS technology for RF applications. The NRE HBT stacks were grown by metal-organic vapor-phase epitaxy on 300 mm Si (001) wafers with a double trench-patterned oxide template, in an industrial deposition chamber. Aspect ratio trapping in the narrow bottom part of a trench results in a threading dislocation density below 106∙cm−2 in the device layers in the wide upper part of that trench. NRE is used to create larger area NRs with a flat (001) surface, suitable for HBT device fabrication. Transmission electron microscopy inspection of the HBT stacks revealed restricted twin formation after the InGaP emitter layer contacts the oxide sidewall. Several structures, with varying InGaP growth conditions, were made, to further study this phenomenon. HBT devices—consisting of several nano-ridges in parallel—were processed for DC and RF characterization. A maximum DC gain of 112 was obtained and a cut-off frequency ft of ~17 GHz was achieved. These results show the potential of NRE III–V devices for hybrid III–V/CMOS technology for emerging RF applications.

Strain Modulation of Selectively and/or Globally Grown Ge Layers

This article presents a novel method to grow a high-quality compressive-strain Ge epilayer on Si using the selective epitaxial growth (SEG) applying the RPCVD technique. The procedures are composed of a global growth of Ge layer on Si followed by a planarization using CMP as initial process steps. The growth parameters of the Ge layer were carefully optimized and after cycle-annealing treatments, the threading dislocation density (TDD) was reduced to 3 × 107 cm−2. As a result of this process, a tensile strain of 0.25% was induced, whereas the RMS value was as low as 0.81 nm. Later, these substrates were covered by an oxide layer and patterned to create trenches for selective epitaxy growth (SEG) of the Ge layer. In these structures, a type of compressive strain was formed in the SEG Ge top layer. The strain amount was −0.34%; meanwhile, the TDD and RMS surface roughness were 2 × 106 cm−2 and 0.68 nm, respectively. HRXRD and TEM results also verified the existence of compressive strain in selectively grown Ge layer. In contrast to the tensile strained Ge layer (globally grown), enhanced PL intensity by a factor of more than 2 is partially due to the improved material quality. The significantly high PL intensity is attributed to the improved crystalline quality of the selectively grown Ge layer. The change in direct bandgap energy of PL was observed, owing to the compressive strain introduced. Hall measurement shows that a selectively grown Ge layer possesses room temperature hole mobility up to 375 cm2/Vs, which is approximately 3 times larger than that of the Ge (132 cm2/Vs). Our work offers fundamental guidance for the growth of high-quality and compressive strain Ge epilayer on Si for future Ge-based optoelectronics integration applications.

Improving Transport Properties of GaN-Based HEMT on Si (111) by Controlling SiH4 Flow Rate of the SiNx Nano-Mask

The AlGaN/AlN/GaN high electron mobility transistor structures were grown on a Si (111) substrate by metalorganic chemical vapor deposition in combination with the insertion of a SiNx nano-mask into the low-temperature GaN buffer layer. Herein, the impact of SiH4 flow rate on two-dimensional electron gas (2DEG) properties was comprehensively investigated, where an increase in SiH4 flow rate resulted in a decrease in edge-type threading dislocation density during coalescence process and an improvement of 2DEG electronic properties. The study also reveals that controlling the SiH4 flow rate of the SiNx nano-mask grown at low temperatures in a short time is an effective strategy to overcome the surface desorption issue that causes surface roughness degradation. The highest electron mobility of 1970 cm2/V·s and sheet carrier concentration of 6.42 × 1012 cm−2 can be achieved via an optimized SiH4 flow rate of 50 sccm.

On the Study of Dislocation Density in MBE GaSb-Based Structures

The results of the study on threading dislocation density (TDD) in homo- and heteroepitaxial GaSb-based structures (metamorphic layers, material grown by applying interfacial misfit array (IMF) and complex structures) deposited using molecular beam epitaxy are presented. Three measurement techniques were considered: high-resolution x-ray diffraction (HRXRD), etch pit density (EPD), and counting tapers on images obtained using atomic force microscopy (AFM). Additionally, high-resolution transmission electron microscopy (HRTEM) was used for selected samples. The density of dislocations determined using these methods varied, e.g., for IMF-GaSb/GaAs sample, were 6.5 × 108 cm−2, 2.2 × 106 cm−2, and 4.1 × 107 cm−2 obtained using the HRXRD, EPD, and AFM techniques, respectively. Thus, the value of TDD should be provided together with information about the measurement method. Nevertheless, the absolute value of TDD is not as essential as the credibility of the technique used for optimizing material growth. By testing material groups with known parameters, we established which techniques can be used for examining the dislocation density in GaSb-based structures.