The growth of high In content InGaN material is notorious for being challenging because of high mechanical strain and thermodynamic instability of the system. It has been shown that one can improve the growth quality by using variable surface miscut. In this study, we demonstrate the use of micropatterning of bulk GaN substrates in order to improve the quality of high In content layers. During MOVPE growth the quality of the InGaN layers and the In content depends on the local shape of the substrate surface, reaching the highest emission intensity at the top of every pattern. We study patterns with characteristic sizes ranging from 1 to 6 µm created using two methods: binary photolithography combined with a thermal reflow process as well as multilevel photolithography. The latter allows for achieving lower inclination of the sidewall of the pattern which in turn supports a more stable growth process. The properties of the samples are studied using fluorescence microscopy, microphotoluminescence mapping and carrier diffusion measurements.
The goal of this work lies in expanding the integrated circuit technology to short wavelengths with the use of nitride emitters. We propose an approach that allows monolithic fabrication of lasers and waveguides using the same epitaxial structure. This is achieved by increasing the misorientation of the substrate locally, prior to the epitaxy, which allows local modification of the indium incorporation into the InGaN layers. Such areas are then used for etching down waveguides with low absorption. Within this work, we develop our technology for the fabrication of waveguide combiners, which involves creating waveguides with bends that bring two or more optical modes into close proximity. We compare systems consisting of 1 mm long laser diodes coupled to 1 mm bent waveguides with bend angles from 2.5° to 45° and different bend radiuses. We estimate the losses based on the optoelectrical parameters of the working system, treating it as a laser diode with a passive region introducing optical losses.
In this paper, we try to resolve problems related to decreasing the size of an LED, and find a solution that would let us preserve optoelectronics parameters. The main idea is to use tunnel junctions to define the current path and, therefore, define the size of µLED. This way, during fabrication, there is no need to etch the active region. That way, it does not introduce any degradation nor problems related to surface states or differences in electrical fields inside the device.
We have fabricated such devices with sizes ranging from 100 µm-5 µm. In the characterization of these devices, it became apparent that, both electrical and optical parameters, are fully scalable with size. Most importantly, we do not observe an increase in the non-radiative recombination coefficient even for the smallest device. In addition, we observe excellent thermal stability of their light emission characteristics.
In this work, we study the optoelectrical properties of nitride LED structures employing polarization doping for the p-type layers. We compare standard Mg-doped, partially doped, and undoped AlGaN p-type layers. The electrical properties of these samples are similar, proving the successful use of polarization doping. The optical measurements suggest that doping of the electron blocking layer is required for preserving good light emission efficiency. We also studied our samples at lowered temperatures and observed no freeze-out region down to 77K. For top metal contact, sub contact doping is indispensable because the intrinsic top layer causes the Schottky barrier.
Our goal is to fabricate a laser diode 2D array which combines the properties of both VCSEL and edge emitting laser. Proposed light emitter will have a horizontal cavity with 450 deflectors. The role of these deflectors would be to deflect light perpendicular to the cavity, achieving vertical out-coupling. The most challenging part of this project is the fabrication of the micro-mirrors which act as both as beam deviating mirrors and cavity forming mirrors. Owing to the excellent thermal conductivity of GaN substrates the properties of such a 2D array should be better than of conventional nitride laser diode arrays, not even mentioning nitride-based stacked bars systems. In this paper I will describe our new device design and processing, giving insight to its possible applications and advantages over simple light emitting laser diode.
KEYWORDS: Semiconductor lasers, Waveguides, Gallium nitride, Waveguide lasers, Near field optics, High power lasers, Laser applications, Gallium, Diodes, Quantum optics
The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from UV, ~380 nm, to the visible ~530 nm, by tuning the indium content of the laser GaInN quantum well. This makes nitride laser diodes suitable for a vast range of applications, but most of them require not only the proper wavelength emission, but also high optical power and good beam quality. The typical approach - wide ridge waveguide - often suffers from spatial multimode emission (low beam quality). We report our initial results with tapered GaN lasers to increase the maximum optical power of the device with a good beam profile. This combination opens new possibilities for GaN laser diode technology in quantum technologies including optical atomic clocks and quantum gravity sensors.
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