Superconductors

Integration of superconductors with semiconductors is required for high-performance electron devices in new quantum, sensing, and systems applications. In article number 1900675, D. Scott Katzer and co-workers report the fully epitaxial integration of III-N and GaN HEMT structures on superconducting transition metal nitrides. Image created by Robert Kurcoba using an atomic image provided by Ph.D. student Yimo Han and Professor David Muller at Cornell University.

Chemical Etching

This figure is a schematic drawing of the experimental setup and principle of the synchrotron X-ray topography used for the observation of dislocations in β-Ga₂O₃ crystal. Two types of surface orientation of the samples are indicated in the crystal structure of β-Ga₂O₃ visualized by VESTA software. More details can be found in article number 1900630 by Yongzhao Yao and co-workers.

Molecular beam epitaxy is used to grow epitaxial III-N and GaN high electron mobility transistor (HEMT) structures directly integrated with epitaxial transition metal nitride materials. The growth conditions used, and the physical and electronic properties of the films are reported, including the first epitaxial integration of GaN HEMT transistors with an epitaxial superconducting load.

Indium phosphide (InP) membrane photonics on silicon (IMOS) combines the high-density nanophotonic circuitries and the high-efficiency direct-bandgap optoelectronics in a single micrometer-thick membrane layer. It enables strong light-matter interaction in the membrane, leading to a range of performance enhancements. Integrating this InP membrane on electronics wafer will enable revolutionary cointegration and convergence of photonics and electronics.

Chemical etching and synchrotron X-ray topography (XRT) are used to evaluate crystallographic defects in β-Ga₂O₃ substrates grown by edge-defined film-fed growth. Dislocations and stacking faults are revealed by etching in a eutectic molten KOH + NaOH solution at 200 °C for 2 min. Correlation between the positions of the etch features and defects are confirmed by XRT.

The molecular beam epitaxy growth of GaSb on Ge (111) vicinal substrates is performed with Bi irradiation. The effects of the Bi irradiation on the surface morphology and on the crystallinity are investigated using atomic force microscopy and X-ray diffraction, respectively. It is shown that Bi works as a surfactant, which suppresses the generation of rotational twins in the GaSb layer.

Herein, vertical β-Ga₂O₃ Schottky barrier diodes (SBDs) with an ion-implantation-based planar edge termination structure are developed and their switching performance is also investigated. The devices exhibit greatly enhanced reverse blocking characteristics and fast switching performance. The results indicate a great promise of vertical β-Ga₂O₃ SBDs for high-voltage fast switching applications.

A simple and low-cost fabrication technique is proposed for CH₃NH₃PbBr₃-based perovskite single-crystal arrays by combining spin coating and a hydrophobic/hydrophilic patterned substrate. By optimizing the substrate surface treatment, blending ratio of precursor solution, and spinning condition, the precursor solution is uniformly aligned on a hydrophobic pattern area and perovskite single crystals are precipitated at the center of the pattern area.

Herein, lattice-matched InGaAs solar cells grown on InP substrates via solid-source molecular beam epitaxy are investigated. It is found that the growth at 490 °C on InP(001) miscut 2° toward (111)A promotes step-flow growth, resulting in less nonradiative recombination. As a result, the lowest bandgap−open-circuit voltage deficit of 369 mV is obtained.

The photodiode for the methane gas sensor is fabricated in the AlInSb/GaAs system. Inserting optimized dislocation filter layers (DFLs) decreases the dislocation density in the active layer to 1.1 × 10⁹cm⁻². This improvement produces a normal incidence detectivity of 1.8 × 10⁹ cm √Hz W⁻¹ at 3.3 μm, which is more than twice the highest detectivity previously obtained for a photodiode without DFLs.

Unstrained Ga_1–xIn_xSb quantum well (QW) channel using strained-Al_0.40In_0.60Sb/Al_1–yIn_ySb stepped buffer layer is investigated. The Ga_1–xIn_xSb QW is lattice-matched to the Al_1–yIn_ySb lower buffer layer. The Te-δ-doped Al_0.40In_0.60Sb barrier layer is grown on the Ga_1–xIn_xSb QW. Sheet electron density (N_s) of Ga_1–xIn_xSb QW is about twice that of InSb one. Thus, increasing N_s while keeping relatively high electron mobility is successful.

Ge-doped GaN is grown by pulsed laser deposition with pico-second laser. Incorporation of laser braking not only improves growth uniformity with a carrier density of 3.5 × 10²⁰ cm⁻³ but also achieves to fabricate non-alloy ohmic. In addition, the laser blanking results in complete elimination of Ga droplet even at the growth temperature of 500 °C.

Degradation of electrical properties is observed for aluminum-doped zinc oxide (AZO) thin films exposed to a harsh environment. Recovery is achieved by reannealing the degraded AZO films in a hydrogen atmosphere at 400–550 °C. This indicates that the degradation mechanism involves chemical aspects such as diffusion of water molecules, which is reversible, rather than physical damage to the films.

The regional control of bandgap energies using the highly stacked quantum dot (QD) on InP(311)B substrate changing ion implantation depths in the process of the quantum dot intermixing (QDI) technique is investigated. Controlled blue shifts of the photoluminescence (PL) spectra verify effectiveness of the regionally controlled QDI process for application to semiconductor photonic integrated circuits using 1550 nm-band QD.

Epitaxial growth of AlGaInAs-based multiquantum wells heterostructure on a directly bonded InP-SiO₂/Si substrate is evaluated. The thermal strain induced in the bonded membrane is assessed from in situ curvature measurement carried out during growth. Ex situ characterizations account for the high crystal quality of the structure compared to a reference grown on InP substrate.

The design, fabrication, and performance of buried-tunnel junction (BTJ) current injection structures for InP/Si hybrid photonic crystal surface emitting lasers (PCSELs) are reported. Corresponding BTJ-light-emitting diodes on InP substrate show low series resistance and uniform carrier injection, whereas BTJ-PCSEL structures with similar current injection configuration fabricated on photonic-crystal silicon-on-insulator substrate using transfer print technology show significant linewidth narrowing at low current.

The fabrication process of a gate dielectric using poly(methyl methacrylate) (PMMA) solution in a fluorine-based solvent onto the active layers based on various semiconductors without intermixing can be applied to top-gated organic light-emitting transistors. For a device with Pt-tetraphenyltetrabenzoporphyrin [Pt(tpbp)] doped in poly(9,9-dioctylfluorene) (F8), a near-infrared emission from Pt(tpbp) and a relatively high external quantum efficiency of approximately 1% are achieved.

The successful operation of an enhancement/depletion (E/D)-type inverter consisting of n-channel enhancement- and depletion-mode MOSFETs (E-MOSFET and D-MOSFET) fabricated on a low Mg concentration p-GaN layer on GaN substrate with a maximum voltage gain 1.5 beyond unity is presented. Study of Si ion-implantation effects on GaN for GaN-based monolithic inverter is also reported.

Over 150-nm-thick AlGaInN films near alloy compositions lattice-matching to GaN on sapphire are grown by metalorganic chemical vapor deposition, and they showed relatively flat surfaces regardless of their lattice strains. Their crystal mosaicity probably depended on that of the underlying GaN films. Optical characterization results indicated that there is a certain degree of compositional fluctuation in the films.

A method to determine the intersystem crossing rate (k_ISC) in thermally activated delayed fluorescence (TADF) emitters is reconsidered. Since the method widely used in the literature may cause errors at low temperatures, an alternative approach is devised. The k_ISC values determined with this approach for two TADF emitters from 10 to 300 K are also presented.

A prototype of an artificial tactile sense of a soft robot finger which is expected to substitute sensitive human finger and to be engaged in high precision works is proposed. Curved surface consisting of thermally molded plastic film is effective because it has smooth shape that is realistic to the original 3D designed mold.

Quasi-phase-matched orientation-patterned GaP (OP-GaP) is a promising technology for mid-infrared and terahertz frequency generation. This work investigates the heteroepitaxy of OP-GaP on OP-GaAs template to exploit their complementary beneficial properties. By mitigating the adverse impact of lattice mismatching defects on the development of domain boundaries, OP-GaP with a high domain fidelity is obtained on OP-GaAs with a high growth rate.

The peculiarities of heavily boron-doped germanium, selectively grown at low temperature by means of a cyclic deposition and etch chemical vapor deposition process, are investigated through the analysis of the structural and electrical material properties. The experimental studies are supported by first principles simulations which are used to understand dopant deactivation mechanisms in the Ge:B system.

Designing a hydride vapor-phase epitaxy reactor for bulk GaN growth is a challenging task where issues of chemical resistance, uniformity, repeatability, and long nonstop growth should be addressed. A quartz-free reactor with external precursor sources and a vacuum load-lock chamber is developed and tested in operation with more than a thousand growth processes performed.

Growth and electrical property of conductive Sn-doped α-Ga₂O₃ films on m-plane sapphire by mist chemical vapor deposition (mist-CVD) are exhibited. α-Ga₂O₃ films on m-plane sapphires with the thickness of 2 μm show mobility as high as 65 cm² (V s)⁻¹, which is much higher than previously reported value of 24 cm² (V s)⁻¹ in the films grown on c-plane sapphire.