GaN-based VCSEL Research Articles

Study of Ga-Polar and N-Polar GaN-Based Green VCSELs by Simulation

Study of Ga-Polar and N-Polar GaN-Based Green VCSELs by Simulation

GaN-Based VCSELs with A Monolithic Curved Mirror: Challenges and Prospects

In this paper, we introduce how gallium nitride-based (GaN-based) VCSELs with curved mirrors have evolved. The discussion starts with reviewing the fundamentals of VCSELs and GaN-based materials and then introducing the curved-mirror cavity’s principle and history and the latest research where the structure is applied to GaN-based materials to form VCSELs. We prepared these parts so that readers understand how VCSELs with this cavity work and provide excellent characteristics such as efficiency, life, stabilized mode behavior, etc. Finally, we discussed the challenges and prospects of these devices by touching on their potential applications.

Narrow Divergence Emission from Blue GaN-based VCSELs with Curved Mirror

Recently, research to achieve narrow emission from GaN-based VCSELs has been of great interest. Sony's VCSELs with curved mirror has feature of strong lateral optical condiment, in which, causes wider emission angle. The authors obtained narrow emission angle of 3.9 degree by adopting concave mirror with large radius of curvature.

Transferrable dielectric DBR membranes for versatile GaN-based polariton and VCSEL technology

We present an innovative process to realize planar GaN microcavities, based on transferrable high-quality oxide-based Distributed-Bragg-Reflector (t-DBR) membranes. Unlike the widely used direct DBR deposition, which is not always feasible, the concept of t-DBR membranes allows their versatile use as top mirrors in all kinds of vertical-cavity surface emitting geometry devices, including light emitting diodes and lasers. The process illustrated here starts by evaporating first a 4-pair SiO2/Ta2O5 DBR centered around 400 nm on a lithographically patterned GaAs substrate. The GaAs substrate is subsequently removed by wet-etching, and the released DBR membranes are transferred onto other templates for their use as top mirrors in microcavities. By transferring a 4-pair top DBR on an 8-pair bottom SiO2/Ta2O5 DBR, a distinct cavity mode appears due to the formed λ/2 oxide cavity with a Q-factor of 110. If the 4-pair top DBR is transferred on 200 nm-thick GaN/AlGaN quantum well-containing membranes sitting on 10-pair bottom DBRs, complete all-dielectric nitride polariton structures are fabricated with pronounced strong-coupling characteristics.

Sub-milliampere-threshold continuous wave operation of GaN-based vertical-cavity surface-emitting laser with lateral optical confinement by curved mirror

The continuous wave operation of a gallium-nitride-based vertical-cavity surface-emitting laser (GaN-based VCSEL) that uses boron ion implantation for lateral current confinement and a curved mirror for lateral optical confinement was investigated. The threshold current was 0.25 mA (Jth = 3.5 kA cm−2) for a 3 μm diameter current aperture at room temperature and the lasing wavelength was 445.3 nm. This is the lowest threshold current recorded for a GaN-based VCSEL. This result is considered to be a milestone for the further miniaturization of GaN-based VCSELs by the implementation of lateral optical confinement due to the incorporation of a curved mirror.

GaN-based Vertical-Cavity Surface-Emitting Lasers Incorporating Dielectric Distributed Bragg Reflectors

This paper reviews past research and the current state-of-the-art concerning gallium nitride-based vertical-cavity surface-emitting lasers (GaN-VCSELs) incorporating distributed Bragg reflectors (DBRs). This paper reviews structures developed during the early stages of research into these devices, covering both major categories of GaN-based VCSELs: hybrid-DBR and all-dielectric-DBR. Although both types exhibited satisfactory performance during continuous-wave (CW) operation in conjunction with current injection as early as 2008, GaN-VCSELs have not yet been mass produced for several reasons. These include the difficulty in controlling the thicknesses of nitride semiconductor layers in hybrid-DBR type devices and issues related to the cavity dimensions in all-dielectric-DBR units. Two novel all-dielectric GaN-based VCSEL concepts based on different structures are examined herein. In one, the device incorporates dielectric DBRs at both ends of the cavity, with one DBR embedded in n-type GaN grown using the epitaxial lateral overgrowth technique. The other concept incorporates a curved mirror fabricated on (000-1) GaN. Both designs are intended to mitigate challenges regarding industrial-scale processing that are related to the difficulty in controlling the cavity length, which have thus far prevented practical applications of all-dielectric GaN-based VCSELs.

Lateral optical confinement of GaN-based VCSEL using an atomically smooth monolithic curved mirror

We demonstrate the lateral optical confinement of GaN-based vertical-cavity surface-emitting lasers (GaN-VCSELs) with a cavity containing a curved mirror that is formed monolithically on a GaN wafer. The output wavelength of the devices is 441–455 nm. The threshold current is 40 mA (Jth = 141 kA/cm2) under pulsed current injection (Wp = 100 ns; duty = 0.2%) at room temperature. We confirm the lateral optical confinement by recording near-field images and investigating the dependence of threshold current on aperture size. The beam profile can be fitted with a Gaussian having a theoretical standard deviation of σ = 0.723 µm, which is significantly smaller than previously reported values for GaN-VCSELs with plane mirrors. Lateral optical confinement with this structure theoretically allows aperture miniaturization to the diffraction limit, resulting in threshold currents far lower than sub-milliamperes. The proposed structure enabled GaN-based VCSELs to be constructed with cavities as long as 28.3 µm, which greatly simplifies the fabrication process owing to longitudinal mode spacings of less than a few nanometers and should help the implementation of these devices in practice.

Thermal lensing effects on lateral leakage in GaN-based vertical-cavity surface-emitting laser cavities.

Lateral leakage of light has been identified as a detrimental loss source in many suggested and experimentally realized GaN-based VCSELs. In the present work we include thermal effects to realistically account for the substantial Joule heating in these devices. In contrast to what could be expected from the previous results, the induced thermal lensing does not make antiguided cavities more positively guided, so that they approach the unguided regime with extremely high lateral leakage. Rather, thermal lensing strongly suppresses lateral leakage for both antiguided and guided cavities. This is explained in terms of lowered launch of power from the central part of the cavity and/or lower total internal reflection in the peripheral part; the former effect is active in all cavities whereas the latter only contributes to the very strongly reduced leakage in weakly antiguided cavities. Thermal lensing suppresses lateral leakage both for the fundamental and the first higher order mode, but a strong modal discrimination is still achieved for the antiguided cavities. Thus, strongly antiguided cavities could be used to achieve single-mode devices, but at the cost of slightly higher threshold gain and stronger temperature dependent performance characteristics.

GaN基蓝光VCSEL的制备及光学特性

GaN基蓝光VCSEL的制备及光学特性

Analysis of structurally sensitive loss in GaN-based VCSEL cavities and its effect on modal discrimination

Lateral loss causes optical energy to leave the laser cavity in the transverse, lateral, direction, and is sometimes neglected to simplify the numerical simulations. However, in contrast to outcoupling and absorption losses, we show that the lateral loss can change drastically with only nanometer-sized changes of the cavity structure, from being virtually zero to becoming the major source of cavity loss, since the cavity becomes antiguiding. This can be explained as the opening of a channel of efficient resonant lateral leakage of optical power at a certain oblique propagation angle. A number of different realizations of current apertures and top mirror designs in GaN-based VCSEL cavities, which have been suggested for realization of microcavity lasers emitting in the blue wavelength range, are simulated. Many of these are shown to lead to unintentional antiguiding, which can more than double the threshold gain for lasing. Notably, for strong enough antiguiding the resonant lateral leakage decreases so that the threshold gain values might again be tolerable. This regime has been suggested for robust single-mode operation since earlier predictions, building on analogies with slab waveguides, hinted at a very strong suppression of higher order modes. However, our simulations indicate that for the VCSEL cavities the derived formulas grossly overestimate the modal discrimination.

The effect of oxide aperture diameter on the electrical characteristics of the GaN-based vertical cavity surface emitting laser

In this paper, a numerically investigation of the aperture diameter in intracavity-contacted oxide-confined GaN-based VCSEL is presented. Simulation results show that with increasing of the current aperture diameter, there is a reduction in the differential resistance of the VCSEL. The influence of oxide aperture on the threshold current has also been investigated. There is an enhancement in the threshold current of the VCSEL by increasing the oxide aperture diameter.

Number of Quantum Well(s) Effects on GaN-Based VCSELs

Number of Quantum Well(s) Effects on GaN-Based VCSELs