We experimentally demonstrate and elucidate by numerical simulations that breaking circular symmetry of large apertures of vertical-cavity surface-emitting lasers (VCSELs) significantly enhances their emission properties by increasing the optical density of states. Specifically, deformed shapes of circular oxide apertures of VCSELs enhance stimulated emission and suppress undesired non-radiative recombination contributing to an increase in output optical output power of more than 60% and in quantum efficiency of more than 10%. Our example deformed VCSEL structures demonstrate that the optical density of states appears to be of high importance for conventional optoelectronic devices in accordance to the predictions of quantum electrodynamics theory.
Transparent electrodes implemented on semiconductors are essential components of optoelectronic devices, however, overcoming Fresnel limit and approaching perfect optical transmission together with high electrical conductivity are still a challenge. In this talk, by numerical simulations, we demonstrate a simple polarization-independent mechanism of infrared light funneling through subwavelength one-dimensional metal grating electrode integrated with monolithic high-contrast grating (MHCG). We show optical transmission of 97% through the electrode implemented at the interface between air and high refractive index semiconductor for radiation from broad infrared spectrum and revealing excellent electrical properties determined by sheet resistance below 1 Ohm/Sq.
Transparent electrodes are essential components of optoelectronic devices, however, increasing requirements with respect to transmission at a level approaching 100% and sheet resistance below 1 Sq-1 are still a challenge. In this talk, we show that monolithic deep-subwavelength grating integrated with metal enables to reach those requirements for broad spectrum of polarized light. It facilitates injection of very high current densities exceeding 20 kA cm-2 not causing noticeable heat generation that meets the requirements of the most demanding optoelectronic devices such as semiconductor lasers.
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.
III-N-based edge-emitting lasers suffer from low refractive index contrast between GaN, AlGaN and InGaN layers, conventionally used in their epitaxial structures. This issue becomes more severe with an increase in wavelength at which those devices operate when tuning from blue-violet to real blue and green light. To overcome this issue and to increase the refractive index contrast other materials must be employed within the epitaxial structures replacing the standard nitride layers with materials with lower refractive index. We demonstrate results of effective-index numerical calculations performed for the state-of-the-art semipolar real blue (471 nm) and green (518 nm) edge-emitting lasers with structural modifications that include ITO, AlInN, plasmonic GaN:Ge and nanoporous GaN layers. Such solutions are extensively investigated for III-N-based EELs operating in blue-violet region but only separately. Using combination of these solutions we managed to increase optical confinement factor over twice in blue- and over 3.5-times in green-EELs.
A concept and numerical study of a continuous-wave (CW) nitride-based vertical-external-cavity surface-emitting laser (VECSEL) with an InGaN/GaN active region is presented. The structure is designed to generate radiation around 450 nm. An array of nitride-based continuous-wave laser diodes is proposed to pump directly the quantum wells in the active region. We expect that it enables CW operation of the presented laser, in contrast to the GaN-based VECSELs demonstrated so far. Moreover, employing in-well pumping instead of barrier pumping reduces pump-laser quantum defect, which contributes to better thermal properties of the device. An external efficiency as high as 26% can be theoretically achieved by using a special multi-pass pump setup.
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.
Carrier transport and optical properties of optically pumped vertical-external-cavity surface-emitting lasers (VECSELs)
have been analyzed with the aid of the self-consistent numerical model. An influence of active-region design parameters,
such as its length as well as number and arrangement of quantum wells, on a carrier distribution and material gain has
been investigated. Moreover, a performance of various structures has been compared with the aid of a simple optical
model. In particular, increasing number of quantum wells has been found not always to lead to an increasing maximal
output power. An arrangement of quantum wells is also of importance. For example, quantum wells located in long
active regions far from a chip surface can be not sufficiently pumped. Numerical models described in this paper may
give an opportunity to understand more deeply details of VECSEL operation and to design optimal laser structures.
In the following paper a simulation of optically pumped vertical external cavity surface emitting lasers (VECSEL) with a
novel approach for the improvement of the heat management is presented. In recent VECSEL structures, it was common
to use one top diamond heat spreader in order to decrease the thermal resistance of the device by redistributing the heat
flow to the lateral regions and thus transporting heat down to the copper heat sink more efficiently. We present here
further improvement of the heat management by eliminating the bottom DBR from the heat flow path and substituting it
for a diamond with a High Contrast Grating (HCG). Hence the active region, which consists of 5 pairs of AlGaInAs
quaternary alloy quantum wells, is sandwiched between two diamond heat spreading layers.
The structure of Si HCG deposited on a diamond provides broad wavelength range in which reflectivity is close to 100%
for the emitted beam for perpendicular mode polarization with respect to the direction of the HCG trenches. The HCG
assures less than 20% reflection and near zero absorption of pumping light, hence it allows for on-axis bottom pumping
scheme and integration of the VECSEL with the pumping laser. According to the simulations 300 μm thick top diamond
heat spreader is enough to assure effective heat dissipation mechanism. Replacing the bottom DBR with the diamond
heat spreader will provide additional 10% reduction of the thermal impedance. The minimum of thermal impedance is
achieved for about 450 μm thick bottom diamond heat spreader.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.