Showing papers in "Physica Status Solidi (a) in 2020"

Indium phosphide membrane nanophotonic integrated circuits on silicon

Abstract: Photonic integration in a micrometer-thick indium phosphide (InP) membrane on silicon (IMOS) offers intrinsic and high-performance optoelectronic functions together with high-index-contrast nanophotonic circuitries. Recently demonstrated devices have shown competitive performances, including high side-mode-suppression ratio (SMSR) lasers, ultrafast photodiodes, and significant improvement in critical dimensions. Applications of the IMOS devices and circuits in optical wireless, quantum photonics, and optical cross-connects have proven their performances and high potential.

Vertical β-Ga 2 O 3 Schottky Barrier Diodes with Enhanced Breakdown Voltage and High Switching Performance

Abstract: Herein, vertical Schottky barrier diodes (SBDs) based on a bulk beta-Ga2O3 substrate are developed. The devices feature an ion-implanted planar edge termination (ET) structure, which can effectively smoothen the electric field peak and reduce the electric field crowding at the Schottky junction edge. Greatly enhanced reverse blocking characteristics including approximate to 10(3)x lower reverse leakage current and 1.5x higher breakdown voltage (V-B) are achieved, whereas good forward conduction such as a reasonably high on-state current density and near-unity ideality factor is maintained. In addition, the switching performance of the fabricated vertical beta-Ga2O3 SBDs is investigated using a double-pulse test circuit. When switching from an on-state current of 350 mA to a reverse-blocking voltage of -100 V, the vertical beta-Ga2O3 SBDs exhibit fast reverse recovery with a reverse recovery time (t(rr)) of approximate to 14.1 ns and reverse recovery charge (Q(rr)) of approximate to 0.34 nC, outperforming the Si fast recovery diode (FRD) of similar ratings. The results indicate a great promise of vertical beta-Ga2O3 SBDs for high-voltage fast switching applications.

Status and Prospects of AlN Templates on Sapphire for Ultraviolet Light‐Emitting Diodes

Abstract: In recent years ultraviolet (UV) light-emitting diodes (LEDs) entered several fields of applications, e.g., phototherapy, water disinfection, biochemical agent detection, and gas sensing. These Al(In)GaN-based LEDs are not only environmental friendly replacements for mercury lamps but also open up new applications due to their compactness, narrow line width, and rapid turn-on/turn-off behavior. For some applications in the UVB (320–280 nm) and UVC (280–200 nm) spectral range, e.g., medical treatment, water purification, and nonline-of-sight communication, UV LEDs with high powers and high efficiencies are needed. Unfortunately, in this wavelength range, the devices still suffer from obstacles like limited UV transparency of native AlN bulk substrates or high densities of threading dislocations (TDs) in layers grown on foreign substrates. These TDs lead to nonradiative recombination in the active region. Especially for shorteremission wavelength with increasing Al content in the AlGaN layers challenges are the poor p-type conductivity, decreasing charge carrier confinement with increasing Al content in the active region, and an increasing amount of TMpolarized light, making light extraction more difficult. In this article, we will focus on the improvement of the efficiency of such LEDs by improving the properties of the templates on which they are grown. As bulk AlN with sufficient UV transparency is not readily available, a pseudosubstrate is commonly used, which consists of AlN and AlGaN layers grown on sapphire substrates by vapor phase epitaxy (Figure 1). Such pseudosubstrates have to fulfil four key requirements. 1) A low threading dislocation density (TDD) preferably below 10 cm , e.g., to reduce nonradiative recombination in the LED active region; 2) surface morphology suitable for further growth, particularly smooth enough for n-AlGaN and quantum well (QW) growth with a well-defined and homogeneous composition; 3) transparency for the emitted UV light, as due to large p-metal contacts and, in case of UVC LEDs also due to nontransparent p-AlGaN, the LEDs are usually fabricated as bottom emitters (i.e., emission through the pseudosubstrate, as shown in Figure 1); and 4) offering a defined in-plane lattice constant which allows for the pseudomorphic growth of the QW region without the onset of relaxation processes (e.g., roughening or dislocation formation). In the first part of this article, we provide an overview on template technologies including the approaches which we have explored in detail in our group. In the second part, we provide insights into our current routes for further template improvement. Even if semiand nonpolar AlGaN could have advantages by reducing or avoiding piezoelectric fields and in promoting light extraction of the TM-polarized deep UVC light, this work focuses on the commonly used c-plane Al(Ga)N grown by metal–organic vapor phase epitaxy (MOVPE) on c-plane-oriented sapphire substrates. Dr. S. Hagedorn, S. Walde, Dr. A. Knauer, D. Pacak, Dr. C. Netzel, Dr. A. Mogilatenko, Prof. M. Kneissl, Prof. M. Weyers Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany E-mail: Markus.Weyers@fbh-berlin.de N. Susilo, D. Pacak, Dr. T. Wernicke, Prof. M. Kneissl Institute of Solid State Physics Technical University Berlin Hardenbergstr. 36, 10623 Berlin, Germany L. Cancellara, Dr. C. Hartmann Leibniz Institute for Crystal Growth Max-Born-Str. 2, 12489 Berlin, Germany

AlGaN/GaN Superlattice-Based p-Type Field-Effect Transistor with Tetramethylammonium Hydroxide Treatment

Abstract: To realize the full spectrum of advantages that the III-nitride materials system offers, the demonstration of p-channel III-nitride based devices is valuable. Authors report the first p-type field effect transistor (pFET) based on an AlGaN/GaN superlattice (SL), grown using MOCVD. Magnesium was used as the p-type dopant. A sheet resistance of 11.6 k{\\Omega}/sq, and a contact resistance of 14.9{\\Omega}.mm was determined using transmission line measurements (TLM) for a Mg doping of 1.5e19cm^-3 of Mg. Mobilities in the range of 7-10 cm\\^2/Vs and a total sheet charge density in the range of 1e13-6e13 cm-2 were measured using room temperature Hall effect measurements. Without Tetramethylammonium hydroxide (TMAH) treatment, the fabricated pFETs had a maximum drain-source current (IDS) of 3mA/mm and an On-Resistance (RON) of 3.48 k{\\Omega}.mm, and did not turn-off completely. With TMAH treatment during fabrication, a maximum IDS of 4.5mA/mm, RON of 2.2k{\\Omega}.mm, and five orders of current modulation was demonstrated, which is the highest achieved for a p-type transistor based on (Al,Ga)N.