InGaN-based Laser Research Articles

480 nm InGaN-based cyan laser diode grown on Si by interface engineering of active region

InGaN-based long wavelength laser diodes (LDs) grown on Si are highly desirable for expanding the applications in laser display and lighting. Proper interface engineering of high In-content InGaN multi-quantum wells (MQWs) is urgently required for the epitaxial growth of InGaN-based long wavelength LD on Si, because the deteriorated interfaces and crystalline quality of InGaN MQWs can severely increase the photon scattering and further exacerbate the internal absorption loss of LDs, which prevents the lasing wavelength of InGaN-based LDs from extending. In this work, a significantly improved morphology and sharp interface of the InGaN active region are obtained by using a graded-compositional InGaN lower waveguide (LWG) capped with a 10-nm-thick Al0.1Ga0.9N layer. The V-pits density of the InGaN LWG was one order of magnitude reduction from 4.8 × 108 to 3.6 × 107 cm-2 along with the root-mean-square surface roughness decreasing from 0.3 to 0.1 nm. Therefore, a room-temperature electrically injected 480 nm InGaN-based cyan LD grown on Si under pulsed current operation was successfully achieved with a threshold current density of 18.3 kA/cm2.

Optimal waveguide structure for low-threshold InGaN/GaN-based photonic-crystal surface-emitting lasers

We analyzed the optimal waveguide structure of two types of InGaN-based photonic crystal surface-emitting lasers (PCSELs) to suppress the coupling with leaky modes via mode simulations. To minimize the threshold material gain (gth), we calculated the confinement factor and quality factor of PCSELs with varying waveguide layer thicknesses in the separate confinement heterostructure (SCH) layer. The optical mode intensity profile revealed the coupling between the fundamental mode of SCH and parasitic leaky modes in the cladding layer or substrate as the primary root cause of the low-quality factor and high threshold gain of PCSELs. The asymmetric nature of the SCH structure yielded the optimal waveguide structure to be dependent on the position of the air holes. With a proper waveguide thickness and air hole depth, the optimized threshold modal gain of PCSELs with the n-side air holes can be less than 30 cm−1.

Spontaneous Emission Studies for Blue and Green InGaN-Based Light-Emitting Diodes and Laser Diodes

We investigated the efficiency droop phenomenon in blue and green GaN-based light-emitting diodes (LEDs) and laser diodes (LDs), which poses a significant challenge in high-power LEDs and is characterized by a reduction in external quantum efficiency at higher injection currents. Utilizing identical epi-structures for blue and green LEDs and LDs, with variations only in indium composition, our experiments revealed a gradual blue shift in the emission wavelengths as the injection current increased. Notably, the blue LED demonstrated a smaller shift compared to the green LED. In addition, the full width at half maximum of emission spectra increased with increasing injection current density, indicative of efficiency droop. Significantly, LDs consistently exhibited lower junction temperatures despite operating at higher current densities. This is attributed to the enhanced heat dissipation capability of the ridge waveguide LD structure, which results in a narrower emission spectrum and reduced efficiency droop compared to mesa LED structures. These outcomes highlight the efficiency of the ridge waveguide LD structure in heat dissipation from the active layer, offering crucial insights for the advancement of high-power light-emitting devices.

Effect of metallurgical step-graded quantum barrier on the performance of InGaN-based laser diode

In this paper, a metallurgical step-graded uniform quantum barrier (QB) laser diode (LD) structure is proposed, which leads to performance enhancement in terms of reduced electron seepage current, reduced threshold current, diminished polarization charges at interfaces, and increased laser power, hole injection efficiency, optical confinement etc. The proposed LD structure demonstrated the best results among all the three structures considered in this study. The laser output power was increased from 118 mW to 160 mW in the metallurgical step-graded uniform QB LD structure as compared to the ungraded QB reference structure. The optical confinement was improved from 0.94% to 1.09% in the photon-generating region. The electron potential barrier height has increased from 191 meV to 242 meV, while the hole potential barrier height has decreased from 133 meV to 116 meV at 120 mA injection current. In addition, the electron seepage flux has reduced from 1374 A cm−2 to 768 A cm−2 at 120 mA injection current.

The critical impact of the waveguide thickness on the optical and threshold behaviors of InGaN-based green laser diodes

We study the optical structures of green (520 nm) InGaN-based laser diodes (LDs) with the complex 1D transfer matrix method, in consideration of the anti-guiding effect and mode leakage into the substrate. Two characteristic thicknesses of the waveguide are found to play critical roles in the behavior of the LD threshold and the beam quality. When a minimum threshold is desired, there exists an optimal thickness (OT) of the waveguide, which is strongly affected by the index contrast of the structure and the anti-guiding factor of the active region. A proper waveguide thickness (WT) makes the structure more tolerant of the mode leakage and the anti-guiding effect. An intrinsic failure in the lasing mode emerges with improper WTs. When a complete elimination of the substrate mode is desired, the waveguide above a critical thickness (CT) is required. To compromise the threshold and the beam quality, an eclectic thickness, while a high composition in the waveguide is suggested.

Low threshold current density and high power InGaN-based blue-violet laser diode with an asymmetric waveguide structure.

Performance of InGaN-based blue-violet laser diodes (LD) with different waveguide structure were investigated by simulation and experimental methods. Theoretical calculation demonstrated that threshold current (Ith) can be reduced and slope efficiency (SE) can be improved by using an asymmetric waveguide structure. Based on the simulation results, a LD with 80-nm-thick In0.03Ga0.97N lower waveguide (LWG) and 80-nm-thick GaN upper waveguide (UWG) is fabricated with flip chip package. Under continuous wave (CW) current injection at room temperature, its optical output power (OOP) reaches 4.5 W at an operating current of 3 A and the lasing wavelength of 403 nm. The threshold current density (Jth) is 0.97 kA/cm2 and the SE is about 1.9 W/A.

Research on Optimization of p-Type Waveguide Layer and Active Region of InGaN-Based Blue Laser Diodes

Research on Optimization of p-Type Waveguide Layer and Active Region of InGaN-Based Blue Laser Diodes

Effect of In Mole Fraction in Upper Waveguide Layer on Performance of InGaN-Based Blue Lasers

Effect of In Mole Fraction in Upper Waveguide Layer on Performance of InGaN-Based Blue Lasers

Comparative investigation into key optoelectronic characteristics of semipolar InGaN blue laser diodes: A strategy to mitigate quantum-confine stark effect

In recent years, semipolar InGaN-based blue laser diodes (LDs) have raised indescribable appeal within solid-state lighting industry as promising alternatives for currently available polar c-plane LDs due to reduction in internal polarization field and related quantum-confined stark effect. However, any comparative study in terms of energy band gap, optical emission profile, power output (P) and forward bias response (I-V) etc. between semipolar-oriented InGaN blue LDs is inherently unattainable. This work aims to demonstrate the impact of internal polarization field on aforementioned key optoelectronic parameters of In0.17Ga0.83N/GaN double quantum well (DQW) blue LD along semipolar (101-2), (112-2), (101-1), (202-1), (303-1-), (202-1-) and (101-1-) crystal orientations by figuring out six-band k.p Hamiltonian at the brillouin zone center aided from Euler’s tensor transformation method. Three-level rate equations based LD analogous circuit model and state-space matrix are employed here to obtain P-I-V and frequency characteristics. Radiative as well as non-radiative recombination mechanisms for LD systems are portrayed by addressing modified ABC model. Our numerical investigation illustrates that best hole effective mass, optical gain, lasing power, threshold current and forward voltage can be attained from (112-2)-oriented InGaN blue LD due to insignificant presence of spontaneous plus piezoelectric (PZ) polarization charge. In addition with these, the inspection of bode plot and relevant optical power gain (dB) confirms the stability and superiority of this semipolar blue LD system for achieving high-speed visible-light communications at relatively low current densities.

Composition-graded quantum barriers improve performance in InGaN-based laser diodes

InGaN laser diodes (LDs) with composition-graded (CG) quantum barriers (QBs) are proposed and our study of them described. In the CG QB LDs, the indium content x in the In x Ga1-x N QB was increased gradually along the growth direction. Their laser power–current–voltage performance curves, carrier concentrations, energy band diagrams, current distributions, electrostatic fields, and stimulated recombination rate in the active region were studied. It is shown that the laser power increases from 59.8 mW to 106.9 mW at 120 mA and the slope efficiency increases from 0.76 W A−1 to 1.27 W A−1, when the conventional GaN QBs are replaced by the proposed CG QBs. The simulation results indicate that LDs with CG QBs performed better than LDs with conventional GaN QBs and InGaN QBs because the suppression of electron leakage is more efficient, as is hole injection and carrier-stimulated recombination in multiple quantum wells through the appropriate formation of polarization energy band structures.

Enhancement of deep violet InGaN double quantum wells laser diodes performance characteristics using superlattice last quantum barrier

Abstract The performance characteristics of InGaN double-quantum-well (DQW) laser diodes (LDs) with different last barrier structures are analyzed numerically by Integrated System Engineering Technical Computer Aided Design (ISE TCAD) software. Three different kind of structures for last quantum barrier including doped- GaN, doped- AlGaN and GaN/AlGaN superlattice last barrier are used and compared with conventional GaN last barrier in InGaN-based laser diodes. Replacing the conventional GaN last barrier with p-AlGaN increased hole flowing in the active region and consequently the radiative recombination which results in the enhancement of output power. However it caused increasing the threshold current due electron overflowing. For solving this problem, the last barrier structure altered with GaN/AlGaN superlattice. The simulation indicates that the electrical and optical characteristics of LDs with the superlattice last barrier, like output power, differential quantum efficiency (DQE) and slope efficiency, has significantly improved, besides the threshold current decreased. The enhancement is mainly attributed to the improvement of hole injection and the blocking electron overflowing which are caused by the reduction of polarization charges at the interface between the barrier and well, and electron blocking layer (EBL).

Narrow linewidth near-UV InGaN laser diode based on external cavity fiber Bragg grating

We realize a fiber Bragg grating InGaN-based laser diode emitting at 400 nm and demonstrate its high coherency. Thanks to the fabrication of a narrowband fiber Bragg grating in the near-UV, we can reach single-mode and single-frequency regimes for the self-injection locked diode. The device exhibits 44 dB side-mode suppression ratio and mW output power. Detailed frequency noise analysis reveals sub-MHz integrated linewidth and 16 kHz intrinsic linewidth. Such a narrow linewidth laser diode in the near-UV domain with a compact and low-cost design could find applications whenever coherency and interferometric resolutions are needed.

Characteristics of InGaN-based green laser diodes with additional InGaN hole reservoir layer

The injection of holes has an important impact on the performance of InGaN-based green laser diodes (LDs). In this work, we propose a new structure with InGaN hole reservoir layer (HRL) inserted between the last quantum barrier and the upper waveguide to improve the hole injection. It is found that the hole injection current is significantly increased due to the reduction of the hole effective barrier height. Furthermore, lower threshold current and higher output power are obtained, and the optical field leakage is effectively suppressed. Besides, the influences of thickness and In composition of the HRL are also investigated. It is more favorable to improve the properties of LDs when the HRL has a quite low-In content and a thickness of only nearly 11 nm.

Atomistic modeling of InGaN/GaN quantum dots-in-nanowire for graded surface-emitting low-threshold, blue exciton laser

While the development of the quantum photonics field, including emitter–light coupling using photonic system, has given a lot of attention, it offers quantum control of light. However, the main challenge is coupling to strongly photonic mode localization with nanosystem accuracy. This paper highlights the numerical simulations employed by atomically spin tight-binding model of realistically sized InGaN/GaN dots-in nanowire (NW) architectures. The effects of active region size/shapes, crystal growth directions, graded surface/interface properties, strain relaxation distributions, and polarization-induced potentials on the oscillator strengths of InGaN-based lasers have been investigated. The 3D nanofocused photonic modes, which have been deterministically coupled to multiple quantum dots (QDs) through graded surface/interface technique, have been demonstrated. By using a thin graded layers of a site-controlled pyramidal QDs, the photonic nanofocusing on these QDs at the nonpolar pyramid apex has been geometrically accomplished and successfully leads to stronger characteristics in terms of exciton bandgap energy and polarized emission rate compared to its polar counterpart. For optimum coupling, the nonpolar NW, with intrinsically lower built-in field, exhibits an enhancement of the QDs emission rate as high as 0.98, which is 12% greater than that in a recently reported semipolar MQD structure. The atomistic simulated emission rate for the core QDs buried in NW structure is then incorporated into a TCAD simulator to obtain laser device characteristics. Here, the achievement of truncated pyramid–electrically injected graded surface-emitting laser by nanofocusing the photonic modes formed in InGaN NW has been reported. The nonpolar laser device operates at ~ 402 nm and exhibits a threshold current of ~ 391 A/cm2, which is lower nine order of magnitude lower compared to recently reported semipolar green laser diodes. Our model benchmarking has been done against a reported experiment of polar InGaN disks in GaN NW. Significantly, this engineering innovation proves the viability of InGaN nonpolar quantum dots-in-nanowire architecture as low threshold, high polarized, coherent blue nanoscale lasing emitters, and opens future trends toward a next-generation of electrically injected and interfacial grading-emitting nanolasers operating at high-frequency up to a GHz range.

Improving optical and electrical properties of InGaN-based green laser diodes by graded-compositional waveguide structure

A graded-compositional waveguide structure is proposed to improve the optical field distribution of InGaN-based green laser diodes (LDs). It is found that the optical field leaking into the GaN substrate is suppressed obviously when using the graded-compositional upper and lower waveguide. Owing to the enhancement of refractive index contrast between the waveguide layer and the cladding layer, the optical field confinement factor increases, and the optical field is more concentrated near the active region. Besides, higher output power and lower threshold current are achieved due to reduced electron leakage and increased hole injection. This work provides a theoretical design method for obtaining high-performance InGaN-based green LDs. • A new structure with graded-compositional upper and lower waveguide is proposed. • The optical field leaking into GaN substrate is obviously reduced. • High output power and low threshold current are achieved. • The photoelectric performance of green LDs is significantly improved.

InGaN-Based Lasers with an Inverted Ridge Waveguide Heterogeneously Integrated on Si(100)

Highly efficient electrically injected light source on exact Si(100) has been the bottleneck of Si photonics for decades. InGaN-based laser with a direct bandgap may serve as an efficient on-chip l...

Efficiency enhancement in InGaN-based laser diodes using an optimized Al0.12Ga0.88N electron blocking layer

In this paper, a design for an electron blocking layer (EBL) is proposed to enhance the wall plug efficiency of InGaN-based laser diodes. Using calibrated 3D simulations (including thermal models), a comprehensive analysis of various design aspects (composition, thickness and p-doping) of EBLs is conducted, including their impact on carrier (electron and hole) wavefunction overlap and stimulated recombination rate in the quantum wells (QWs) along with the space charge density, electric field and free carrier absorption (FCA) at the interface of the p-side waveguide/EBL. The results indicate that Poole–Frenkel emission is vital for consideration of FCA in the p-doped layers of the epitaxial structure. Consequently, the proposed EBL design reduces electron overflow, improves hole injection, decreases the internal absorption losses and thus, enhances the internal quantum efficiency of the device. The threshold current is reduced from 230 mA to 205 mA as compared to the reference structure. The hole barrier is reduced by 23.93%. Hence, the output power is increased from 1.746 W to 1.95 W, and the voltage drop as well as the device temperature is reduced. These improvements enhance the efficiency from 37.4% of the reference structure to 42.1% in the proposed structure (corresponding to a bias current of 1 A).

Degradation study of InGaN-based laser diodes grown on Si

The degradation characteristics of InGaN-based laser diodes (LDs) grown on Si substrate have been studied under an electrical stress with a pulsed current of 180 mA. After the electrical stress, the light output power, leakage current and capacitance of the LD decreased, while the operation voltage and threshold current increased, and the slope efficiency remained nearly unchanged after the pulsed electrical stress for 620 h. Further analysis shows that the degradation was probably due to the newly generated group-III vacancies and/or related defects, which can not only act as acceptor-like defects to compensate the n-type donors, leading to the reduction of conductance and capacitance, but also work as non-radiative recombination centers affecting the internal quantum efficiency and emission intensity of the active region.

Continuous-wave electrically injected GaN-on-Si microdisk laser diodes.

Silicon photonics has been calling for an electrically pumped on-chip light source at room temperature for decades. A GaN-based microdisk laser diode with whispering gallery modes grown on Si is a promising candidate for compact on-chip light source. By suppressing the unintentional incorporation of carbon impurity in the p-type AlGaN cladding layer of the laser, we have significantly reduced the operation voltage and threshold current of the GaN-on-Si microdisk laser. Meanwhile the radius of the microdisk laser was shrunk to 8 µm to lower the thermal power. The overall junction temperature of the microdisk laser was effectively reduced. As a result, the first continuous-wave electrically pumped InGaN-based microdisk laser grown on Si was achieved at room temperature.

480-nm distributed-feedback InGaN laser diode for 10.5-Gbit/s visible-light communication.

In this Letter, we demonstrate a novel distributed-feedback (DFB) InGaN-based laser diode with narrow-linewidth emission at ∼480nm (sky blue) and its application to high-speed visible-light communication (VLC). A significant side-mode suppression ratio (SMSR) of 42.4 dB, an optical power of ∼14mW, and a resolution-limited linewidth of ∼34pm were obtained under continuous-wave operation. A 5-Gbit/s VLC link was realized using non-return-to-zero on-off keying modulation, whereas a high-speed 10.5-Gbit/s VLC data rate was achieved by using a spectral-efficient 16-quadrature-amplitude-modulation orthogonal frequency-division multiplexing scheme. The reported high-performance sky-blue DFB laser is promising in enabling unexplored dense wavelength-division multiplexing schemes in VLC, narrow-line filtered systems, and other applications where single-frequency lasers are essential such as atomic clocks, high-resolution sensors, and spectroscopy. Single-frequency emitters at the sky-blue wavelength range will further benefit applications in the low-path-loss window of underwater media as well as those operating at the H-beta Fraunhofer line at ∼486nm.