Thickness Of p-GaN Layer Research Articles

Impacts of p-GaN layer thickness on the photoelectric and thermal performance of AlGaN-based deep-UV LEDs.

The effects of different p-GaN layer thickness on the photoelectric and thermal properties of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) were investigated. The results revealed that appropriate thinning of the p-GaN layer enhances the photoelectric performance and thermal stability of DUV-LEDs, reducing current crowding effects that affect the external quantum efficiency and chip heat dissipation. The ABC + f(n) model was used to analyse the EQE, which helped in identifying the different physical mechanisms for DUV-LEDs with different p-GaN layer thickness. Moreover, the finite difference time domain simulation results revealed that the light-extraction efficiency of the DUV-LEDs exhibits a trend similar to that of damped vibration as the thickness of the p-GaN layer increases. The AlGaN-based DUV-LED with a p-GaN layer thickness of 20 nm exhibited the best photoelectric characteristics and thermal stability.

The role of p-GaN layer thickness for the evaluation of high-performance and ultrafast GaInN/GaN multiple quantum wells UV photodetectors

To improve the performance of GaInN/GaN multiple quantum wells (MQW) ultraviolet photodetectors (UV-PDs), the thickness of p-GaN layer plays an important role. Thereby, to see the impact of p-GaN layer thickness on epilayer quality and device performances, in the present work, we fabricated two different sets of GaInN/GaN MQW-based UV-PDs by varying the thickness of p-GaN layer and examined their epilayer quality and device performances by employing various adequate measurements. Due to increase of p-GaN layer thickness from 125 nm (PD1) to 250 nm (PD2), the density of threading dislocations increases which in turn declines the photocurrent (Ip) and hence, the external quantum efficiency (EQE) in the higher excitation regime (<372 nm). On the other hand, above 372 nm, the values of Ip and EQE in PD2 are higher compared to PD1, indicating the length of photo-absorption layer is improved. Interestingly, PD2 exhibits the widening of the spectral sensitivity towards the higher wavelength regime. Moreover, the temporal photo-response measurements at different optical powers, bias voltages, and switching frequencies (wavelength of the light source = 385 nm) reveal that PD2 has relatively better performance over PD1. These results imply that the separation of photoexcited electron-hole pairs is easier in PD2 than PD1. The faster carrier separation process in PD2 is ascribed to the exacerbated built-in potential in the heterojunction as confirmed via capacitance-voltage analysis. Finally, current–voltage measurements suggest that the series resistance in PD2 increases due to increase of total film thickness.

Is a thin p-GaN layer possible for making high-efficiency AlGaN-based deep-ultraviolet light-emitting diodes?

In this report, we investigate the impact of a thin p-GaN layer on the efficiency for AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs). According to our results, the light extraction efficiency (LEE) becomes higher with the decrease of the p-GaN layer thickness, which can be ascribed to the decreased absorption of DUV emission by the thin p-GaN layer. Moreover, we also find that the variation trend of external quantum efficiency (EQE) is consistent with that of LEE. Therefore, we can speculate that high-efficiency DUV LEDs can be achieved by using thin p-GaN layer to increase the LEE. However, a thin p-GaN layer can also cause severe current crowding effect and the internal quantum efficiency (IQE) will be correspondingly reduced, which will restrict the improvement of EQE. In this work, we find that the adoption of a current spreading layer for such DUV LED with very thin p-GaN layer can facilitate the current spreading effect. For the purpose of demonstration, we then utilize a well-known p-AlGaN/n-AlGaN/p-AlGaN (PNP-AlGaN) structured current spreading layer. Our experimental and numerical results show that, as long as the current crowding effect can be suppressed, the DUV LED with thin p-GaN layer can significantly increase the EQE and the optical power thanks to the enhanced LEE.

Investigation on threshold voltage of p-channel GaN MOSFETs based on p-GaN/AlGaN/GaN heterostructure* *Project supported by the Key-Area Research and Development Program of Guangdong Province, China (Grant Nos. 2020B010174001 and 2020B010171002), the Ningbo Science and Technology Innovation Program 2025 (Grant No. 2019B10123), and the National Natural Science Foundation of China (Grant No. 62074122).

The threshold voltage (V th) of the p-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) is investigated via Silvaco-Atlas simulations. The main factors which influence the threshold voltage of p-channel GaN MOSFETs are barrier height Φ 1,p, polarization charge density σ b, and equivalent unite capacitance C oc. It is found that the thinner thickness of p-GaN layer and oxide layer will acquire the more negative threshold voltage V th, and threshold voltage |V th| increases with the reduction in p-GaN doping concentration and the work-function of gate metal. Meanwhile, the increase in gate dielectric relative permittivity may cause the increase in threshold voltage |V th|. Additionally, the parameter influencing output current most is the p-GaN doping concentration, and the maximum current density is 9.5 mA/mm with p-type doping concentration of 9.5 × 1016 cm−3 at V GS = –12 V and V DS = –10 V.

Design considerations for normally-off operation in Schottky gate p-GaN/AlGaN/GaN HEMTs

Design criteria for normally-off operation in Schottky gate p-GaN/AlGaN/GaN HEMTs have been investigated. The threshold voltage (Vth) of this structure is determined by the following five parameters: (i) acceptor concentration of p-GaN layer (Na), (ii) thickness of p-GaN layer (dp-GaN), (iii) Al composition of AlGaN layer (Alx), (iv) thickness of AlGaN layer (dAlGaN), and (v) Schottky barrier height at gate metal/p-GaN interface (ΦB). Analytical equations are derived to obtain the quantitative relations of these parameters and dependences of normally-off condition on these parameters are discussed. To derive the analytical equation, two cases are considered in this study, i.e., case 1; thick dp-GaN case, and case 2; thin dp-GaN case. For case 1, the normally-off condition is determined by Alx and dAlGaN, and independent of Na, dp-GaN, and ΦB. While for case 2, it is strongly affected by Na, dp-GaN, and ΦB. It is found that a thicker dp-GaN is needed for a lower Na, and with the increase of dAlGaN at a certain Alx to achieve a normally-off operation. Also, it is found that Alx has to be kept less than 0.26 because higher Alx will cause the electric field across AlGaN layer to exceed 3 MV cm−1, which may lead to breakdown in the AlGaN layer.

Improving the luminous efficiency of gallium nitride-based light-emitting diodes using Ag nanograting structure

In order to improve the traditional gallium nitride (GaN)-light-emitting diode (LED) luminous efficiency, a structure of the GaN-LED is designed based on the local field enhancement of surface plasmon (SP). The principle of improving LED luminous properties using the SP features is described in detail. The factors that affect the light extraction efficiency of this LED structure are simulated with the COMSOL software. The thickness of p-GaN layer, the thickness of indium tin oxide (ITO) layer, the grating period T , the duty ratio r , as well as the shape of the interface between p-GaN and ITO are studied. The normalized radiated powers, the normalized absorbed powers, and the electric field distribution of this structure under different structure parameters have been achieved. The results show that when the thickness of p-GaN layer is 110 nm, the thickness of ITO buffer layer is 120 nm, the period T is 370 nm, the duty ratio is 0.5, and the value of D 1 / T is 0.6. The luminous intensity of LED is higher than that of the traditional LED nearly 43 times and is nearly 36 times higher than that of the Ag nanosphere structure, and SPs can be coupled with the active layer effectively to improve the luminous efficiency of LED, providing a theoretical guide for the preparation of high-performance GaN-LED chips.

Investigation of the p-GaN layer thickness of InGaN-based photoelectrodes for photoelectrochemical hydrogen generation

We investigated photoelectrochemical hydrogen generation using InGaN-based photoelectrodes with different p-GaN layer thicknesses. It was confirmed that the photocurrent density and hydrogen generation can be enhanced at zero bias between the photoelectrode and counterelectrode. We found that the maximum energy conversion efficiency was 2.0% when using an InGaN-based photoelectrode with a 20-nm-thick p-GaN layer; this was one order larger than for a photoelectrode without a p-GaN layer. The p-GaN layer can pull the potential of the InGaN layer upward, leading to efficient electron–hole separation in the photoabsorption layer and improving carrier transfer from the InGaN layer. By measuring incident photon to current efficiency, it was confirmed that the InGaN layer worked as a photoelectrode since the absorption edge wavelength was around 400 nm.

Further emission efficiency improvement of a commercial-quality light-emitting diode through surface plasmon coupling.

It is usually believed that surface plasmon (SP) coupling is practically useful only for improving the performance of a light-emitting diode (LED) with a low intrinsic internal quantum efficiency (IQE). In this Letter, we demonstrate that the performance of a commercial-quality blue LED with a high IQE (>80%) can still be significantly improved through SP coupling based on a surface Ag nanoparticle (NP) structure. The performance improvement of such an LED is achieved by increasing the Mg doping concentration in its p-AlGaN electron blocking layer to enhance the hole injection efficiency such that the p-GaN layer thickness can be significantly reduced without sacrificing its electrical property. In this situation, the distance between surface Ag NPs and quantum wells is decreased and hence SP coupling strength is increased. By reducing the distance between the surface Ag NPs and the top quantum well to 66nm, the IQE can be increased to almost 90% (an ∼11% enhancement) and the electroluminescence intensity can be enhanced by ∼24%.

Effects of p-type GaN thickness on optical properties of GaN-based light-emitting diodes

The influence of p-type GaN (pGaN) thickness on the light output power (LOP) and internal quantum efficiency (IQE) of light emitting diode (LED) was studied by experiments and simulations. The LOP of GaN-based LED increases as the thickness of pGaN layer decreases from 300 nm to 100 nm, and then decreases as the thickness decreases to 50 nm. The LOP of LED with 100-nm-thick pGaN increases by 30.9% compared with that of the conventional LED with 300-nm-thick pGaN. The variation trend of IQE is similar to that of LOP as the decrease of GaN thickness. The simulation results demonstrate that the higher light efficiency of LED with 100-nm-thick pGaN is ascribed to the improvements of the carrier concentrations and recombination rates.

Analysis on the effect of amorphous photonic crystals on light extraction efficiency enhancement for GaN-based thin-film-flip-chip light-emitting diodes

This work showed the liquid-like amorphous photonic crystals (PhCs) can effectively enhance the light extraction efficiency of GaN-based thin-film-flip-chip light-emitting diodes (TFFC LEDs) by the light scattering effect. The finite-difference time-domain (FDTD) method was employed to analyze the light scattering characteristics, numerical studies revealed that the amorphous PhCs can provide omnidirectional scattering, and the transmittances of amorphous PhCs is superior to that of triangular lattice PhCs when the incident angle is in the region 20°≤θ≤35°. The influence of p-GaN layer thickness and the amorphous PhCs feature size on the light extraction efficiency was also studied by 3D-FDTD method systematically. For the proposed amorphous PhCs structure in n-GaN layer, the light extraction efficiency is enhanced by a factor of 1.49 as compared to conventional TFFC LEDs, which shows 1.07 times enhancement in comparison to that of triangular lattice PhCs.

背照射和正照射p-i-n结构GaN紫外探测器的i-GaN和p-GaN厚度设计

研究了i-Ga N和p-Ga N厚度对背照射和正照射p-i-n结构Ga N紫外探测器响应光谱的影响。模拟计算发现:对于背照射结构,适当地减小i-Ga N厚度有利于提高探测器的响应,降低i-Ga N层的本底载流子浓度也有利于提高探测器的响应;p-Ga N的欧姆接触特性好坏对探测器的响应影响不大,适当地增加p-Ga N厚度可以改善探测器性能。而正照射结构则不同,i-Ga N厚度对探测器的响应度影响不大,但欧姆接触特性差将严重降低探测器的响应,适当地减小p-Ga N厚度可以大幅度改善探测器的响应特性。能带结构和入射光吸收的差别导致了正照射和背照射探测器结构中i层和p层厚度的选择和设计不同。

Analysis of light extraction efficiency enhancement for thin-film-flip-chip InGaN quantum wells light-emitting diodes with GaN micro-domes

The enhancement of light extraction efficiency for thin-film flip-chip (TFFC) InGaN quantum wells (QWs) light-emitting diodes (LEDs) with GaN micro-domes on n-GaN layer was studied. The light extraction efficiency of TFFC InGaN QWs LEDs with GaN micro-domes were calculated and compared to that of the conventional TFFC InGaN QWs LEDs with flat surface. The three dimensional finite difference time domain (3D-FDTD) method was used to calculate the light extraction efficiency for the InGaN QWs LEDs emitting at 460nm and 550 nm, respectively. The effects of the GaN micro-dome feature size and the p-GaN layer thickness on the light extraction efficiency were studied systematically. Studies indicate that the p-GaN layer thickness is critical for optimizing the TFFC LED light extraction efficiency. Significant enhancement of the light extraction efficiency (2.5-2.7 times for λ(peak) = 460nm and 2.7-2.8 times for λ(peak) = 550nm) is achievable from TFFC InGaN QWs LEDs with optimized GaN micro-dome diameter and height.

Effect of p-GaN layer thickness on the performance of p-i-n structure GaN ultraviolet photodetectors

We investigated the influence of thickness of p-GaN layer on the performance of p-i-n structure GaN ultraviolet photodetector. Through the simulation calculation，it was found that both the quantum efficiency and dark current of device decrease when employing thicker p-GaN layer，while both the quantum efficiency and dark current increase with decreasing thickness of p-GaN layer. It is suggested that the Schottky contact junction between the metal and p-GaN may be responsible for the incompatible effect. We has to make a suitable choice of the thickness of p-GaN in the device design according to the application requirement.