The design of transparent conductive electrodes (TCEs) for optoelectronic devices requires a trade-off between high conductivity or transmittivity, limiting their efficiency. This paper demonstrates a novel approach to fabricating TCEs: a monolithic GaAs high contrast grating integrated with metal (metalMHCG). The technology and influence of fabricated different configurations of metalMHCG on the optical parameters will be shown. We will demonstrate above 90% absolute transmittiance of unpolarized light, resulting in 130% transmittance relative to plain GaAs substrate. Despite record high transmittance, the sheet resistance of the metalMHCG is several times lower than any other TCE, ranging from 0.5 to 1 OhmSq−1.
We present an extensive experimental analysis of two-dimensional gallium-arsenide-based VCSEL arrays considering the impact on performance of the VCSEL density (inter-VCSEL spacing and mesa diameters), the number and arrangement of VCSEL elements, and the VCSEL vertical epitaxial design. We include computer simulations that explain well the behavior and trends we observe in our experiments. We present the most efficient modifications of the lateral and vertical VCSEL arrays designs to optimize heat dissipation, optical output power scaling, and wall plug efficiency.
In this paper, we present numerical simulations of nitride tunnel junction VCSELs (Vertical-Cavity Surface-Emitting Laser). This analysis concerned lasers emitting 405 nm wavelength. The simulated VCSEL is similar to the structure fabricated at University of California, Santa Barbara (UCSB). This structure has an Al-ion implantation applied for outer regions of the cavity. The results show how threshold parameters (threshold temperature and threshold current) and emitted power depend on the contrast of the refractive index in this implantation. We also analyze the influence of the implantation thickness and dimensions of the electrical aperture of the laser on capacitance phenomena occurring in the laser.
In this work, we present numerical simulation of over-threshold characteristics of a GaN-based tunnel-junction verticalcavity surface-emitting laser similar to the device developed at the University of California, Santa Barbara [1]. This structure has dual dielectric mirrors, and a bottom ring contact which additionally works as a heat spreader. Moreover, to introduce confinement of current and optical mode, the additional implantation is applied for outer regions of the cavity. The results show how the number of pairs in the top mirror influence the power emitted by the device. We found that for 11 pairs in the top DBR, which is 1 pair less than for the basic structure, the maximal output power is the highest and is equal to 0.2 mW. We also investigate the impact of the carrier injection efficiency, which can be treated as a fitting parameter in described model, on power-current characteristics.
In this paper, we present a novel design of a nitride-based VCSEL emitting at 414 nm and perform numerical analysis of optical, electrical and thermal phenomena. The bottom mirror of the laser is a Al(In)N/GaN DBR (Distributed Bragg Reflector), whereas the top mirror is realized as a semiconductor-metal subwavelength-grating, etched in GaN with silver stripes deposited between the stripes of the semiconductor grating. In this monolithic structure simulations show a uniform active-region current density on the level of 5.5 kA/cm2 for the apertures as large as 10 μm. In the case of a broader apertures, e.g. 40 μm, we showed that, assuming a homogeneous current injection at the level of 5.5 kA/cm2 , the temperature inside the laser should not exceed 360 K, which gives promise to improve thermal management by uniformisation of the current injection.
Here we investigate the influence of the p- and n-oxide-aperture radii in all-semiconductor GaAs-based verticalcavity surface-emitting lasers (VCSELs), designed for 980 nm, on the modulation time constant (τ). Our analysis shows that the minimum value of τ is obtained if the oxide layers on both sides of the junction have identical depths. The simulations of the number of oxide layers on both p- and n-type sides reveal that double p- and n-oxidations are the most effective in the reduction of the modulation time constant as compared to single oxide layers.
This paper presents results of numerical simulations of a GaAs-based vertical-cavity surface-emitting laser, emitting at 980 nm. These simulations concern the influence of the number of top DBR pairs on the laser’s threshold parameters, as well as the optical loses in the cavity. Moreover, electrical parameters such as the device’s resistance and its capacitance-related temporal characteristics are analyzed as functions of the thickness of the top DBR. The simulations suggest that there is a possibility of a significant reduction in the number of pairs in the top DBR that can be beneficial in certain applications.
Record-large modulation bandwidths of 30 GHz and larger have been achieved with state-of-the art directly and indirectly modulated VCSELs and VCSEL arrays. One next big challenge is to make VCSELs viable for integration onto silicon while maintaining large bandwidth values. Various integration schemes of VCSELs might require process variations potentially detrimental for large modulation bandwidths. We present and compare directly modulated oxide-confined top-emitting 980-nm VCSELs processed from one single epitaxial wafer design into four different extracavity and intracavity contact variations.
In this paper, using our model of capacitance in vertical-cavity surface-emitting lasers (VCSELs), we analyze certain differences between an oxide-confined arsenide VCSEL emitting in the NIR region, and a nitride VCSEL emitting violet radiation. In the nitride laser its high differential resistance, caused partially by the low conductivity of p-type GaN material and the bottom contact configuration, is one of the main reasons why the nitride VCSEL has much worse modulation properties than the arsenide VCSEL. Using the complicated arsenide structure, we also analyze different possible ways of constructing the laser’s equivalent circuit.
Two different approaches to developing new laser sources operating in the mid-infrared range based on vertical-external cavity surface-emitting lasers (VECSELs) are studied with the aid of numerical modelling. The first one consists in enhancing a maximal emission wavelength of currently available GaSb-based structures beyond 3 μm. The second approach consists in using dual-wavelength VECSEL (DW-VECSEL), emitting two coaxial laser beams of different wavelengths, to generate radiation from the 3-5 μm spectral range with the aid of difference frequency generation.
In this paper, we present numerical simulations of different types of nitride VCSELs. We analyzed structures with different DBR mirrors and electrical confinements. We compare threshold parameters, including threshold current, threshold temperature and optical field distribution for structures with an ITO contact and structures with tunnel junctions. Lasers emitting blue/violet and green radiation are analyzed from the point of view of their thermal properties.
In this paper, an impact of mounting of structures of nitride laser bars their performance, emitted optical power in particular, is presented. The laser bars of nitride edge-emitting lasers of ridge-waveguide type the InGaN/GaN active areas have been considered. Laser performance has been analysed with the aid of an advanced self-consistent thermalelectrical model, calibrated using experimental data for a single diode laser. The simulated laser bars emit at 408 nm. An optimal number of laser emitters and their various arrangments have been considered. An appliation of Cu heat sinks of various dimensions as well as the p-side-up or the p-side-down laser configurations have been analysed. Moreover a possible application of a diamond heat spreader has been also taken into account.
In this paper we analyze the influence of the thickness of two oxide layers in a typical oxide-confined vertical-cavity surface-emitting laser (VCSEL) on the capacitance of the device and its electrical modulation properties. An analysis of the distribution of the potential and the energy of the electric field in this device is presented, and the influence of these fields on the laser's capacitance is described. It is shown that the oxide layer closest to the active region contributes in a very different way to the laser's capacitance compared to the second slightly more distant oxide layer, and a quantitative analysis of the impact of the thicknesses of these layers on the modulation time constants is presented.
In this paper we present the simulation results of an oxide-confined, InGaAs/GaAs based vertical-cavity surface-emitting laser with three different configurations of the oxide apertures. We analyze the impact of the number and position of oxide layers on the carrier distribution in the laser's active region, distribution of the optical modes, and modulation properties.
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