Laser power converters (LPCs) based on InxGa1-xAs/GaAs metamorphic heterostructure grown by MOVPE have been investigated. Both direct study of transmission electron microscopy images and analysis of ...the dark I–V curves at a low photogenerated current have shown the absence of the effect of threading dislocations from the metamorphic buffer on the LPC parameters. It has been shown, according to the “voltage” and “current” invariants that voltage loss in all investigated LPCs evidences the good quality of p-n junctions for the operating mode of high power laser radiation conversion. It has been also demonstrated that the method of saturation current approximation with current invariant allows obtaining the limit voltage losses irrespective of photogenerated current. Band-gap and thickness of the InGaAs LPCs have been adjusted using spectral characteristics. Fundamental losses (thermal and resistive) and ways to minimize them have been discussed. As a result, LPCs based on In0.23Ga0.77As have demonstrated the laser conversion efficiency (λ = 1064 nm) of more than 50% with maintaining the efficiency of more than 48% up to 13 W/cm2.
•InxGa1-xAs/GaAs metamorphic laser power convertors (LPCs) were created by MOVPE.•Threading dislocations from step graded buffer do not affect the I–V characteristics.•LPC voltage loss has been estimated by voltage and current invariants.•Structure design optimized for quantum efficiency increase at wavelength of 1064 nm.•LPCs have demonstrated laser conversion efficiency (1064 nm) of more than 50%.
Modal absorptions in laser-like heterostructures containing InAs self-assembled quantum dots (QDs) and InGaAs quantum well-dots (QWDs) have been studied. The evaluation of photoresponse as a function ...of waveguide length has allowed us to determine per-layer modal absorptions of 69 and 13 cm -1 for the ground state optical transitions of QWDs and QDs, respectively. The values of the modal absorption can be used as a measure of the maximal (saturated) modal gain. To compare quantum heterostructures with different dimensionality we have introduced the layer gain constant, a parameter characterizing the light transmittance through the absorbing or gaining layer. We have shown that the QWD layer gain constant significantly exceeds quantum well and quantum dot ones.
We review epitaxial formation, basic properties, and device applications of a novel type of nanostructures of mixed (0D/2D) dimensionality that we refer to as quantum well-dots (QWDs). QWDs are ...formed by metalorganic vapor phase epitaxial deposition of 4–16 monolayers of InxGa1−xAs of moderate indium composition (0.3 < x < 0.5) on GaAs substrates and represent dense arrays of carrier localizing indium-rich regions inside In-depleted residual quantum wells. QWDs are intermediate in properties between 2D quantum wells and 0D quantum dots and show some advantages of both of those. In particular, they offer high optical gain/absorption coefficients as well as reduced carrier diffusion in the plane of the active region. Edge-emitting QWD lasers demonstrate low internal loss of 0.7 cm−1 and high internal quantum efficiency of 87%. as well as a reasonably high level of continuous wave (CW) power at room temperature. Due to the high optical gain and suppressed non-radiative recombination at processed sidewalls, QWDs are especially advantageous for microlasers. Thirty-one μm in diameter microdisk lasers show a high record for this type of devices output power of 18 mW. The CW lasing is observed up to 110 °C. A maximum 3-dB modulation bandwidth of 6.7 GHz is measured in the 23 μm in diameter microdisks operating uncooled without a heatsink. The open eye diagram is observed up to 12.5 Gbit/s, and error-free 10 Gbit/s data transmission at 30 °C without using an external optical amplifier, and temperature stabilization is demonstrated.
We report on the transverse single-mode emission from InGaAs/GaAs quantum well edge-emitting lasers with broadened waveguide. The lasers are based on coupled large optical cavity (CLOC) structures ...where high-order vertical modes of the broad active waveguide are suppressed due to their resonant tunneling into a coupled single-mode passive waveguide. The CLOC lasers have shown stable Gaussian-shaped vertical far-field profiles with a reduced divergence of ∼22° FWHM (full width at half-maximum) in CW (continuous-wave) operation.
Material gain of InGaAs/GaAs quantum well-dots Gordeev, Nikita Yu; Maximov, Mikhail V; Payusov, Alexey S ...
Semiconductor science and technology,
01/2021, Letnik:
36, Številka:
1
Journal Article
Recenzirano
We study material gain of a novel type of quantum heterostructures of mixed (0D/2D) dimensionality referred to as quantum well-dots (QWDs). To evaluate the material gain in a broad range of injection ...currents (30-1200 A cm−2 per-layer) we studied edge-emitting lasers with various numbers of InGaAs/GaAs QWD layers in the active region and different waveguide designs. The dependence of the material gain on the current is well fitted by an empirical exponential equation similar to the one used for quantum dots (QDs) in the whole range of injection current densities. The estimated QWD transparency current-density-per-layer of 31 A cm−2 ranks between the values reported for quantum wells and QDs. The maximal QWD material gain as high as 1.1⋅104 cm−1 has been measured. The results obtained confirm specific gain properties of InGaAs QWDs making them promising active media for lasers, superluminescence diodes and optical amplifiers.
We report on the fabrication and studies of Ø100 μm half-disk lasers with an active region based on InGaAs/GaAs quantum dots providing very high modal gain. Such resonators support whispering gallery ...modes propagating at the cavity periphery. The microlasers show directional light outcoupling: continuous-wave output power emitted from the flat side reaches 17 mW, which is about 7 times greater than the power emitted from the back semicircular side. Single-mode lasing in a wide range of the injection currents is observed. P-side down bonding of the devices onto Si-board allowed increasing the maximum optical power to more than 30 mW and the lasing was observed up to 93°C. The 3 dB modulation bandwidth of 4.6 GHz was measured likely being limited by RC-parasites.
We discuss the effect of self-heating on performance of injection microdisk lasers operating in continuous-wave (CW) regime at room and elevated temperature. A model is developed that allows one to ...obtain analytical expressions for the peak optical power limited by the thermal rollover effect, the corresponding injection current and excess temperature of the device. The model predicts, there exists the maximum temperature of microlaser operation in CW regime and the minimum mircrodisk diameter, at which CW lasing is possible. The model allows one to determine the dependence of the device characteristics on its diameter and the inherent parameters, such as thermal resistance, electrical resistance, non-radiative recombination and characteristic temperature of the threshold current. It is found that a rapid growth of the threshold current density with decreasing the diameter (which takes place even in the absence of the self-heating effect) is the main internal reason leading to the dependence of the temperature characteristics of the mirodisk laser on its size. In the calculations, we used a set of parameters extracted from experiments with InGaAs quantum dot microdisk lasers. The simulation results (in particular, the light-current curve and the dependence of the minimum microdisk diameter on ambient temperature) comply well with the measured dependences.
We discuss the origin of optical losses in microdisk lasers with a dense array of InGaAs quantum dots in the active region. In particular, we study the effect of microlaser diameter <inline-formula> ...<tex-math notation="LaTeX">\mathbf {D} </tex-math></inline-formula> variation from 15 to <inline-formula> <tex-math notation="LaTeX">200~\mu \text{m} </tex-math></inline-formula> on optical losses of different nature. A strong dependence of the lasing wavelength on the diameter is observed: the blue-shift with decreasing disk size implies an increase in optical losses, although in the case of an ideal cylinder, a noticeable optical loss should appear only at diameters comparable to the wavelength of light. A comparison of the spectral characteristics of microlasers with those of broad-area stripe lasers, for which optical loss can be easily found, gives a tool to evaluate optical loss in microdisk lasers, which was found to be unexpectedly high. It changes <inline-formula> <tex-math notation="LaTeX">\boldsymbol {\propto }\mathbf {D}^{\mathbf {-1}} </tex-math></inline-formula> from <inline-formula> <tex-math notation="LaTeX">\sim 100 </tex-math></inline-formula> cm−1 in the smallest microlasers to ~ 5 cm−1 in the largest ones. Several possible physical mechanisms of the appearance of optical losses in microlasers are considered, such as radiative loss due to the curvature of the cylindrical cavity, free carrier absorption, light scattering due to roughness of the side walls, and absorption of light in the near-surface region. The latter type of optical loss was found to be the dominant one and can explain the experimental results once the absorbing layer with a thickness of <inline-formula> <tex-math notation="LaTeX">2~\mu \text{m} </tex-math></inline-formula> was suggested. Using the Gaussian approximation for Using the Gaussian approximation for the gain spectrum, the wavelength-loss relationship was simulated and a good agreement with the experimental dependence was found. The variation of the experimental results on optical loss for nominally identical microlasers was attributed to the variation of the scattering loss. The same reason can explain the scatter of the slope efficiency, which varies from <inline-formula> <tex-math notation="LaTeX">\sim ~0.03 </tex-math></inline-formula> to 0.25 W/A being governed by the ratio of the scattering loss to the surface absorption loss.
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