AlGaN Electron Blocking Layer Research Articles

Controlling GaN-Based Laser Diode Performance by Variation of the Al Content of an Inserted AlGaN Electron Blocking Layer.

The leakage of the electronic current of a laser diode (LD) has some significant influences on the performance of the LD. In this study, commercial simulation software LASTIP is used to numerically evaluate the performances of LDs by using different wavelengths and Al contents of the electron blocking layer (EBL). These LDs a adopt multilayer structure, which contains cladding layers, waveguide layers, multiple quantum well layers, contact layers and an AlxGa1-xN EBL. The influence mechanism of EBL is theoretically examined by analyzing the simulated performances. It is found that for short-wavelength violet LDs, the electrical and optical properties of the LD will reach the optimum state when the Al content (x) in the EBL is nearly 0.25. For long-wavelength green LDs, it will achieve optimum electrical and optical properties when the Al content in the EBL is as low as possible. We also compare the simulation results of LDs with emission wavelengths in the range of violet and green, including blue cyan, for a more general evaluation. According to the simulated results, it is verified that the influence of the EBL's Al content on LD performance enhances as the wavelength increases.

High-Efficiency InGaN Photo Cell Irradiated by 532 nm Laser with AlGaN Electron Blocking Layer

In this paper, a high-efficiency InGaN photo cell irradiated by 532 nm laser (at green wavelength) with AlGaN electron blocking layer (EBL) is proposed based on the blue-green light window effect of seawater. Firstly, the InGaN/GaN multiple quantum wells (MQWs) structured material intercalated with AlGaN EBL was designed and grown for InGaN photo cells. Then, by measuring the AFM, XRD and PL of the material, it is found that the insertion of AlGaN EBL can effectively reduce the defect density and improve the steepness of the interface in the active region. Further, based on the above material characteristics, the performance of the InGaN photo cells with AlGaN EBL is evaluated in Silvaco software under 532 nm laser irradiation. The results show that the introduction of AlGaN EBL in InGaN photo cell can not only decrease the non-radiative recombination rates, but also reduce the piezoelectric polarization effect, which contribute to the transport of effective photo-generated carriers and eventually improve the conversion efficiency by 13.325% compared to that with conventional structure. These findings provide critical new insights on high-efficiency GaN-based Photo Cell irradiated by 532 nm laser in the application of underwater communications.

Designing p-region of AlGaN ultraviolet light-emitting diodes for the improved performance

We have used aluminum indium gallium nitride (AlInGaN) graded layers instead of the conventional combination of three p-type layers i.e., AlGaN final quantum barrier (FQB), AlGaN electron blocking layer (EBL), and top p-AlGaN hole injecting layer to increase the performance of ultraviolet light-emitting diodes (UV LEDs). In this study, the effects of graded quaternary layers (GQLs) on efficiency droop have also been investigated. These GQLs improve the injection of holes into the quantum wells. Our simulated results show that our proposed structure (LED K2) has a high peak efficiency of ∼ 68% and a significantly reduced efficiency droop of ∼41% than LED K1. The radiative recombination rate in the multiquantum wells (MQWs) of LED K2 is improved by ∼90% which can be attributed to enhanced carrier overlap or recombination in the multiquantum wells. The concentration of electrons in the active region of LED K2 is increased by ∼ 56% as compared to LED K1. This is due to the high aluminum (Al) content in GQLs of LED K2 which minimizes the electron leakage.

Performance enhancement with thin p-AlInN electron-blocking layer in ultraviolet light-emitting diodes

III-nitride ultraviolet light-emitting diodes (UV LEDs) face low carrier confinement and poor p-doping. In this study, we propose a thin AlInN electron-blocking layer (EBL) in UV LEDs instead of conventional AlGaN EBL. Numerical results demonstrate that UV LED with thin AlInN enhances the optoelectronic performance. The results also reveal that AlGaN EBL is more sensitive to p-doping as compared to AlInN EBL. Thin AlInN layer facilitates hole transportation through intra-band tunneling. Moreover, AlInN has a high conduction band offset that suppresses the electron leakage effectively. Hence, the carrier radiative recombination rate considerably enhances with thin AlInN EBL. The efficiency droop in the proposed LED is also alleviated.

Suppression of polarization effect in deep-ultraviolet light-emitting diodes with composition-graded triangle electron-blocking layer

Impacts of polarization effect and electron-blocking layer (EBL) on the characteristics of deep-ultraviolet (DUV) light-emitting diode (LED) are investigated numerically. Simulation results show that the DUV LED with a bulk AlGaN EBL of high aluminum composition possesses good capability of electron confinement in general, while the characteristics deteriorate dramatically when the degree of polarization is high. Instead, the DUV LED with a composition-graded triangle AlGaN EBL is found to be less sensitive to the variation of polarization effect and possesses superior output performance in comparison with the counterpart LED with a bulk AlGaN EBL under high degree of polarization. The composition-graded triangle AlGaN EBL is beneficial for the DUV LED with high crystalline quality due to the relatively slight energy band deformation under high degree of polarization.

Compositional degradation of the electron blocking layers through solid-solution in GaN-based laser diodes

Electron leakage currents seriously hinder GaN-based blue laser diodes (LDs) from high wall-plug efficiencies. Inserting an ultra-thin AlGaN electron blocking layer (EBL) in the epitaxy structure is a major technique to suppress the leakage currents for which a high Al composition in the EBL is necessary. Despite many studies on the optimization of the compositions of EBLs, it is questionable whether they reach the designed value in real growths by metal-organic vapor phase epitaxy. We investigate the influence of the growth conditions of upper cladding layers (CLs) on the underlying EBLs. A strong composition degradation of the EBL is observed when the growth rate of the CL is low, which drastically reduces the output performance of both LEDs and LDs. A 30-nm fast-growing protecting layer can efficiently prevent the EBL from such degradation. The phenomenon cannot be explained by a composition pulling effect nor an etch effect by hydrogen, but by a mutual solid solution between the EBL and the adjacent CL. The solution process is found thermally favored by calculating the Gibbs energy where strain and entropies are considered. It is inferred that the chemically active Ga adatoms at the surface play an important role in accelerating the solution process. Based on these considerations, we introduce a random walk model to clarify the kinetic influence of CL growth rates on EBL degradation semi-quantitatively. The results help to understand the subtle process in the growth of heterostructures and the transport process of GaN-based LDs.

Enhanced performance in deep-ultraviolet laser diodes with an undoped BGaN electron blocking layer.

Aluminum-rich p-AlGaN electron blocking layers (EBLs) are typically used for preventing overflow of electrons from the active region in AlGaN-based deep ultraviolet (DUV) laser diode (LD). However, these cannot effectively prevent electron leakage and form barrier layers, which affects the hole injection efficiency. Herein, the traditional p-AlGaN EBL in LD is replaced with an undoped BGaN EBL. The undoped BGaN EBL LD increases the effective barrier height of the conduction band to prevent the leakage of electrons and decreases the energy loss caused by the polarization induced electric field, enhancing the hole injection. The slope efficiency of the undoped BGaN EBL LD is 289% higher than that of the highly doped AlGaN EBL LD, and its threshold current is 51% lower. Therefore, the findings of this study provide insights for solving the problems of electron leakage and insufficient hole injection in high-performance and undoped EBL DUV LDs.

InGaN-based light-emitting diodes with Al content graded p-AlxGa1-xN top contact layer

This study demonstrates a GaN-based light-emitting diode (LED) structure with an Al composition, graded p-Al x Ga 1− x N top contact layer as the electron-blocking layer (EBL). Experimental results showed that the LEDs with graded EBL layer exhibited lower forward voltage ( V f ) and higher output power (L op ) than conventional LEDs with constant Al composition in the EBL. The lower V f is attributed to the relatively higher hole concentration caused by the polarization field in the graded AlGaN EBL. In addition to the improved hole concentration, the higher L op is also due to the improved electron confinement caused by the graded EBL. • GaN-based light-emitting diode (LED) structure possessed an Al composition graded p-AlxGa1-xN top contact layer. • Polarization field in the graded AlxGa1-xN EBL causes the relatively higher hole concentration. • Graded AlGaN EBL could effectively mitigate electrons to overflows to the p-GaN. • LEDs with the graded AlGaN EBL exhibited higher efficiency than conventional LEDs with constant Al in the EBL.

Temperature Dependence of Electron Leakage Current in InGaN Blue Light-Emitting Diode Structures.

We investigated the temperature dependence of the electron leakage current in the AlGaN electron-blocking layer (EBL) of an InGaN/GaN blue light-emitting diode (LED) structure at temperatures between 20 and 100 °C. The percentage of electron leakage current was experimentally determined by fitting the measured external quantum efficiency of an LED using the ABC recombination model. The electron leakage current decreased significantly as the temperature increased from 20 to 100 °C. The experiment obtained temperature-dependent electron leakage current was also found to agree well with the simulation results. This counter-intuitive temperature dependence of the electron leakage current resulted from an increase in potential barrier for electrons with increasing temperature due to the increased ionized acceptor concentration in the EBL with temperature. Moreover, the results obtained for the temperature-dependent electron leakage were consistent with the thermionic emission model. The results of the temperature dependence reported here are expected to provide insight into the thermal droop of GaN-based LEDs.

Optimized carrier confinement in deep-ultraviolet light-emitting diodes with AlInGaN/AlInN superlattice electron blocking layer

The optoelectronic characteristics of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with AlInGaN/AlInN superlattices electron blocking layer (EBL) are numerically investigated. The results show that DUV LED with AlInGaN/AlInN EBL has superior carrier confinement capability over the DUV LED with conventional AlGaN EBL. Hence, the internal quantum efficiency (IQE) and radiative recombination rate of the proposed LED is increased by 49% and 219%, respectively as compared to conventional LED. This is assigned to the optimal recombination of electron-hole pairs in the active zone of the proposed LED. Interestingly, the proposed LED also exhibits near-droop-free efficiency.

A Novel GaN:C Millimeter-Wave HEMT with AlGaN Electron-Blocking Layer.

An AlGaN/GaN/Si high electron mobility transistor (HEMT) using a GaN:C buffer with a 2 nm AlGaN electron-blocking layer (EBL) is investigated for the first time for millimeter-wave applications. Compared with the double heterostructure field effect transistor (DHFET), the AlGaN/GaN HEMT with the GaN:C/EBL buffer has a lower vertical leakage, higher thermal stability, and better RF performance. In addition, AlGaN EBL can prevent carbon-related traps from GaN:C and improve electron confinement in 2DEG during high-frequency operation. Finally, a Pout of 31.2 dBm with PAE of 21.7% were measured at 28 GHz at 28 V. These results demonstrated the great potential of HEMTs using GaN:C with AlGaN EBL epitaxy technology for millimeter-wave applications.

Investigation of the Optimum Mg Doping Concentration in p-Type-Doped Layers of InGaN Blue Laser Diode Structures

In GaN-based laser diode (LD) structures, Mg doping in p-type-doped layers has a significant influence on the device performance. As the doping concentration increases, the operation voltage decreases, whereas the output power decreases as a result of increased optical absorption, implying that optimization of the Mg doping concentration is required. In this study, we systematically investigated the effect of the Mg doping concentration in the AlGaN electron-blocking layer (EBL) and the AlGaN p-cladding layer on the output power, forward voltage, and wall-plug efficiency (WPE) of InGaN blue LD structures using numerical simulations. In the optimization of the EBL, an Al composition of 20% and an Mg doping concentration of 3 × 1019 cm−3 exhibited the best performance, with negligible electron leakage and a high WPE. The optimum Mg concentration of the p-AlGaN cladding layer was found to be ~1.5 × 1019 cm−3, where the maximum WPE of 38.6% was obtained for a blue LD with a threshold current density of 1 kA/cm2 and a slope efficiency of 2.1 W/A.

P-AlInN electron blocking layer for AlGaN-based deep-ultraviolet light-emitting diode

Commonly, the Al-rich AlGaN layer acts as electron blocking layer (EBL) to block the overflow of electrons from the active region in conventional AlGaN deep-ultraviolet (DUV) light-emitting diode (LED). However, the Al-rich AlGaN layer leads to the disadvantages of severe electron overflow and hole blocking effect. Herein, we proposed a new AlInN-based EBL to improve the optoelectronic characteristics of AlGaN-based DUV LED. The calculated results show that conventional (fixed Al composition) AlInN EBL has superior hole injection, reduced electron overflow, and lower electric field as compared to conventional AlGaN EBL. By using AlInN EBL, internal quantum efficiency (IQE) drop is reduced by 20%, and light output power improved by 165.30%. It was noticed that conventional AlInN EBL has a 28% IQE drop which can further be minimized by employing AlInN/AlInN superlattice EBL structure. It is found that superlattice EBL improved carrier distribution and reduced electric field resulting in a higher electron-hole wave-function overlap of 55% within multiple quantum wells (MQW) which elevate radiative recombination rate. AlInN superlattice EBL LED has drop-free 93% IQE, twice light output power, and spontaneous emission rate compared to conventional AlInN EBL LED.

High-performance AlGaN-based deep ultraviolet light-emitting diodes with different types of InAlGaN/AlGaN electron blocking layer

The efficiency performance of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) is restricted by the poor hole injection and severe electron leakage. Here, we propose two types of electron blocking layer (EBL), including InAlGaN/AlGaN EBL and InAlGaN/AlGaN superlattice EBL, to enhance the carrier injection efficiency. We numerically simulated the effect of InAlGaN-based EBL on effective barrier height for carriers. The simulation results reveal that the effective barrier height for carriers can be modulated to be beneficial for electron blocking and hole injection by optimizing In-composition. As a result, the 272 nm DUV LED with InAlGaN/AlGaN EBL exhibits better performance, compared to the DUV LED with AlGaN EBL. What is more, device performance can be further improved when the InAlGaN/AlGaN EBL is replaced by InAlGaN/AlGaN superlattice EBL, due to the latter is more effective to modulate the effective barrier height for carriers when the In-composition is appropriate.

Electron overflow of AlGaN deep ultraviolet light emitting diodes

We have studied the design, epitaxy, and performance characteristics of deep ultraviolet (UV) AlGaN light emitting diodes (LEDs). By combining the tunnel junction and polarization-engineered AlGaN electron blocking layer, a maximum external quantum efficiency and wall-plug efficiency of 0.35% and 0.21%, respectively, were measured for devices operating at ∼245 nm, which are over one order of magnitude higher than previously reported tunnel junction devices at this wavelength. Severe efficiency droop, however, was measured at very low current densities (∼0.25 A/cm2), which, together with the transverse magnetic (TM) polarized emission, is identified to be the primary limiting factors for the device performance. Detailed electrical and optical analysis further shows that the observed efficiency droop is largely due to an electrical effect instead of an optical phenomenon. Our studies suggest that AlGaN deep UV LEDs with efficiency comparable to InGaN blue-emitting quantum wells can be potentially achieved if issues related to electron overflow and TM polarized emission are effectively addressed.

The marvelous optical performance of AlGaN-based deep ultraviolet light-emitting diodes with AlInGaN-based last quantum barrier and step electron blocking layer.

The optoelectronic characteristics of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with quaternary last quantum barrier (QLQB) and step-graded electron blocking layer (EBL) are investigated numerically. The results show that the internal quantum efficiency (IQE) and radiative recombination rate are remarkably improved with AlInGaN step-graded EBL and QLQB as compared to conventional or ternary AlGaN EBL and last quantum barrier (LQB). This significant improvement is assigned to the optimal recombination of electron–hole pairs in the multiple quantum wells (MQWs). It is due to the decrease in strain and lattice mismatch between the epi-layers which alleviates the effective potential barrier height of the conduction band and suppressed the electron leakage without affecting the holes transportation to the active region. Moreover, to figure out quantitatively, the electron and hole quantity increased by ~ 25% and ~ 15%, respectively. Additionally, the IQE and radiative recombination rate are enhanced by 48% and 55%, respectively, as compared to conventional LED. So, we believe that our proposed structure is not only a feasible approach for achieving highly efficient DUV LEDs, but the device physics presented in this study establishes a fruitful understanding of III nitride-based optoelectronic devices.

Hole transport enhancement by thickness- and composition-grading of electron blocking layer

We have numerically examined the advantages of thickness- and composition-grading of the electron blocking layer (EBL) in InGaN multiquantum well light-emitting diodes. We have enhanced the hole confinement inside the active region, which is critical in GaN-based devices. Low hole injection is more severe when conventional wide bandgap AlGaN EBL is inserted between the last GaN quantum barrier and the p-GaN layer. The results obtained show reduced valence band offset leading to improved hole injection and enhanced device performance.

BAlN for III-nitride UV light-emitting diodes: undoped electron blocking layer

The undoped BAlN electron-blocking layer (EBL) is investigated to replace the conventional AlGaN EBL in light-emitting diodes (LEDs). Numerical studies of the impact of variously doped EBLs on the output characteristics of LEDs demonstrate that the LED performance shows heavy dependence on the p-doping level in the case of the AlGaN EBL, while it shows less dependence on the p-doping level for the BAlN EBL. As a result, we propose an undoped BAlN EBL for LEDs to avoid the p-doping issues, which a major technical challenge in the AlGaN EBL. Without doping, the proposed BAlN EBL structure still possesses a superior capacity in blocking electrons and improving hole injection compared with the AlGaN EBL having high doping. Compared with the Al0.3Ga0.7N EBL with a doping concentration of 1 × 1020 cm−3, the undoped BAlN EBL LED still shows lower droop (only 5%), compatible internal quantum efficiency (2% enhancement), and optical output power (6% enhancement). This study provides a feasible route to addressing electron leakage and insufficient hole injection issues when designing ultraviolet LED structures.

Upping the internal quantum efficiency of green light‐emitting diodes by employing a graded AlGaN barrier and an electron blocking layer

Two different device structures are numerically studied, and their optoelectronic characteristics with standard structure are compared. The authors minimized the uneven carrier distribution across the active region. By replacing the first quantum barrier with graded AlGaN and using a graded AlGaN electron blocking layer, in the structure proposed by the authors, the injection of holes into the active region is improved. By using the graded AlGaN barrier, the concentration of injected electrons is also controlled because of the additional barrier height. As a result, the contribution of radiative recombination is boosted. The droop ratio of the proposed structure is reduced to ∼34% at 100 A cm−2 in comparison to other devices.

Alloy segregation at stacking faults in zincblende GaN heterostructures

Current cubic zincblende III-Nitride epilayers grown on 3C-SiC/Si(001) substrates by metal-organic vapor-phase epitaxy contain a high density of stacking faults lying on the {111} planes. A combination of high-resolution scanning transmission electron microscopy and energy dispersive x-ray spectrometry is used to investigate the effects of alloy segregation around stacking faults in a zincblende III-nitride light-emitting structure, incorporating InGaN quantum wells and an AlGaN electron blocking layer. It is found that in the vicinity of the stacking faults, the indium and aluminum contents were a factor of 2.3 ± 1.3 and 1.9 ± 0.5 higher, respectively, than that in the surrounding material. Indium and aluminum are also observed to segregate differently in relation to stacking faults with indium segregating adjacent to the stacking fault while aluminum segregates directly on the stacking fault.