p-InGaN Layer Research Articles

Enhanced luminescence property of GaN-based LEDs with p-InGaN cap layer grown on p-GaN surface

The influence of a p-In0.06Ga0.94N cap layer grown on p-GaN on the device performance of GaN-based light-emitting diodes (LEDs) was investigated. Compared to conventional p-GaN LED structure, the light output power of p-InGaN/GaN structure LED was enhanced by 20% and the operating voltage decreased from 3.81 to 3.29 V under 20 mA injection current. Based on surface morphology and electrical analysis, these improvements were mainly attributed to the higher light extraction efficiency and lower contact resistence. It was observed that V-shaped pits appearing on the surface of p-InGaN increased surface roughness, resulting in higher extraction efficiency. After molten KOH etching to p-InGaN layer, the V-shaped pits became bigger, further increasing surface roughness. The larger surface roughness further increased light output power from 20% to 44%. In addition, the forward voltage under 20 mA increased from 3.29 V to 3.41 V which indicated etching process decreased the surface ohmic contact.

Regulation of Hole Concentration and Mobility and First-Principle Analysis of Mg-Doping in InGaN Grown by MOCVD.

This work studied the regulation of hole concentration and mobility in p-InGaN layers grown by metalorganic chemical vapor deposition (MOCVD) under an N-rich environment. By adjusting the growth temperature, the hole concentration can be controlled between 6 × 1017/cm3 and 3 × 1019/cm3 with adjustable hole mobility from 3 to 16 cm2/V.s. These p-InGaN layers can meet different requirements of devices for hole concentration and mobility. First-principles defect calculations indicate that the p-type doping of InGaN at the N-rich limiting condition mainly originated from Mg substituting In (MgIn). In contrast with the compensation of nitrogen vacancy in p-type InGaN grown in a Ga-rich environment, the holes in p-type InGaN grown in an N-rich environment were mainly compensated by interstitial Mg (Mgi), which has very low formation energy.

High conversion and quantum efficiency indium-rich p-InGaN/p-InGaN/n-InGaN solar cell

In this paper, an efficient three-layered p-In0.6Ga0.6N/p-In0.7Ga0.7N/n-In0.7Ga0.7N (PPN) solar cell was designed. The characteristics of the PPN-junction InGaN solar cell were simulated using the SCAPS-1D software. The effects of the thickness and carrier density of the PPN layer on solar cell performance were evaluated. The results were compared with those of the performance of the PN-junction solar cell. Results revealed that a thin top p-InGaN with a high carrier density had a considerable influence on the performance of the solar cell. Adding a p-InGaN layer as thin as 0.01 μm on the top of the PN-junction solar cell substantially improved the conversion efficiency of the solar cell from 21.39% (PN) to 30.23% (PPN).

Color-tunable <10 μ m square InGaN micro-LEDs on compliant GaN-on-porous-GaN pseudo-substrates

In this study, two methods to tune the emission wavelength of micro-LEDs fabricated on tile patterned compliant GaN-on-porous-GaN pseudo-substrates (PSs) are presented. The mechanical flexibility of porous GaN was utilized to relax the strain induced during the growth of light-emitting diode (LED) structures with n- and p-InGaN layers and enhance the indium incorporation via the composition pulling effect. The first approach involved only varying the size of the PS square tiles used for LED structure regrowth, from 20 × 20 μm2 to 8 × 8 μm2. Higher n-InGaN base layer relaxation with decreasing tile size resulted in a red shift of emission from 525 nm to 561 nm with no change in the growth conditions. The second method involved changing the mole fraction, x, of the n-InxGa1−xN base layer of the LED structure from 0.04 to 0.09 by reducing growth temperature, while maintaining the high temperature growth conditions of the multi-quantum well (MQW) and p-InGaN targeting 530 nm emission. The resulting wavelength shift was a remarkable 536–616 nm due to the stronger composition pulling effect, providing a pathway to enable high indium content MQW active regions to be grown at high temperature.

Numerical Simulation of Single Junction InGaN Solar Cell by SCAPS

The performance of the InGaN single-junction thin film solar cells has been analyzed numerically employing the Solar Cell Capacitance Simulator (SCAPS-1D). The electrical properties and the photovoltaic performance of the InGaN solar cells were studied by changing the doping concentrations and the bandgap energy along with each layer, i.e. n-and p-InGaN layers. The results reveal an optimum efficiency of the InGaN solar cell of ~ 15.32 % at a band gap value of 1.32 eV. It has been observed that lowering the doping concentration NA leads to an improvement of the short circuit current density (Jsc) (34 mA/cm2 at NA of 1016 cm−3). This might be attributed to the increase of the carrier mobility and hence an enhancement in the minority carrier diffusion length leading to a better collection efficiency. Additionally, the results show that increasing the front layer thickness of the InGaN leads to an increase in the Jsc and to the conversion efficiency (η). This has been referred to the increase in the photogenerated current, as well as to the less surface recombination rate.

Influence of Thickness of p-InGaN Layer on the Device Physics and Material Qualities of GaN-Based LEDs With p-GaN/ InGaN Heterojunction

The influence of the thickness of a p-InGaN layer on the device physics and the material qualities of GaN-based light-emitting diodes (LEDs) are investigated in both numerical and experimental ways. A promoted structure of p-GaN/In0.005Ga0.95N (80/120 nm) heterojunction has been found to remarkably improve the LED’s performance. It is demonstrated by the experimental results that the light output power and wall-plug efficiency of such LED increase by 44.63% and 60.66% with a comparison to the conventional LED, respectively. Theoretical calculation reveals that thickening the p-InGaN layer will increase the number of holes accumulating in the p-GaN/InGaN heterojunction and modify the energy band profile of electron blocking layer, which makes it more favorable for carriers to inject into multiple quantum wells (MQWs). However, it is unfortunately found that overthickening the p-InGaN layer will make its crystalline quality degrade and finally affect the MQWs. The thickness of the p-InGaN layer should be carefully controlled at about 120 nm; otherwise, the performance of LED will be severely damaged by the increasing electrical resistance and the enhanced nonradiative recombination in MQWs, which is resulted from the material degradation in p-InGaN layer and MQWs. This paper demonstrates a possibility for achieving high-performance LEDs with the p-GaN/InGaN heterojunction and is of great interest for the commercial development of GaN-based LEDs.

Quantum Efficiency Enhancement of a GaN-Based Green Light-Emitting Diode by a Graded Indium Composition p-Type InGaN Layer.

We propose a graded indium composition p-type InGaN (p-InGaN) conduction layer to replace the p-type AlGaN electron blocking layer and a p-GaN layer in order to enhance the light output power of a GaN-based green light-emitting diode (LED). The indium composition of the p-InGaN layer decreased from 10.4% to 0% along the growth direction. The light intensity of the LED with a graded indium composition p-InGaN layer is 13.7% higher than that of conventional LEDs according to the experimental result. The calculated data further confirmed that the graded indium composition p-InGaN layer can effectively improve the light power of green LEDs. According to the simulation, the increase in light output power of green LEDs with a graded indium composition p-InGaN layer was mainly attributed to the enhancement of hole injection and the improvement of the radiative recombination rate.

GaN-Based Light-Emitting-Diode With a p-InGaN Layer

GaN-based LEDs with a p-InGaN layer was proposed and fabricated. By inserting the 50-nm-thick <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{p-In}_{0.01}\hbox{Ga}_{0.99}\hbox{N}$</tex> </formula> layer, it was found that we could reduce the 20 mA forward voltage from 3.34 to 2.99 V. It was found the inserted p-InGaN layer could also reduce the efficiency droop from 36.7% to 23.8%.

Efficiency and droop improvement in a blue InGaN-based light emitting diode with a p-InGaN layer inserted in the GaN barriers

The advantages of a blue InGaN-based light-emitting diode with a p-InGaN layer inserted in the GaN barriers is studied. The carrier concentration in the quantum well, radiative recombination rate in the active region, output power, and internal quantum efficiency are investigated. The simulation results show that the InGaN-based light-emitting diode with a p-InGaN layer inserted in the barriers has better performance over its conventional counterpart and the light emitting diode with p-GaN inserted in the barriers. The improvement is due to enhanced Mg acceptor activation and enhanced hole injection into the quantum wells.

Characteristics of an Indium-Rich InGaN p—n Junction Grown on a Strain-Relaxed InGaN Buffer Layer

An indium-rich InGaN p—n junction is grown on a strain-relaxed InGaN buffer layer. The results show that the n-InGaN is grown coherently on the buffer layer but the p-InGaN layer exhibits a partial strain relaxation. The fabricated InGaN p—n junction has a low reverse leakage current density on the order of 10−8 A/cm2 within the measured voltage range, and exhibits a wide spectral response due to the presence of band tail states or deep level states which origin from indium composition fluctuation or various defects. The measured peak responsivity at 438 nm is 31 mA/W at zero bias and reaches 118 mA/W at 3V reverse bias. In addition, the Raman spectra of the p- and n-type InGaN alloys are also analyzed.

Structural and electrical characterization of InN, InGaN, and p-InGaN grown by metal-modulated epitaxy

InN, high indium content InGaN, and Mg-doped InGaN were grown by metal modulated epitaxy (MME). Transient reflection high-energy electron diffraction intensities were analyzed during the growth of InN and found to be similar to that previously reported for GaN and AlN. The x-ray diffraction rocking curve and background electron concentration of InN grown by MME were found to be respectable in comparison to recent reports in literature. InGaN alloys grown by MME were also investigated, and a method for detecting indium surface segregation was demonstrated. It was found that the shutter modulation scheme could be modified to prevent phase separation by indium surface segregation, and a range of single-phase InGaN samples with indium contents throughout the miscibility gap were grown. Using the discovered method of suppressing phase separation, several p-InxGa1 − xN samples were grown with indium contents from x = 0 to 0.22. A maximum hole concentration of 2.4 × 1019 cm−3 was detected by Hall effect characterization, demonstrating feasibility of these p-InGaN layers for use in several device applications.

Normally off AlGaN/GaN high electron mobility transistors with p-InGaN cap layer

Normally off AlGaN/GaN HEMTs with a p-In0.23Ga0.77N cap layer were successfully fabricated. The key idea in this approach is to employ the polarization-induced field in the InGaN cap and negative charge in the p-InGaN cap; this raises the conduction band at the AlGaN/GaN interface and leads to normally off operation. A threshold voltage of 1.2 V and maximum transconductance of 146 mS/mm were obtained. The gate leakage current of the InGaN-capped AlGaN/GaN HEMTs was investigated in detail. The V-shaped defects originating from the AlGaN surface have been shown to be responsible for the gate leakage current. The insertion of a thin GaN layer between the p-InGaN and AlGaN layers was shown to be effective in suppressing the formation of V-shaped defects and decreasing the gate leakage current.

Improvements in Microstructure and Leakage Current of High-In-Content InGaN p-i-n Structure by Annealing

The effects of annealing on the microstructure and electrical properties of a high-In-content InGaN p-i-n structure have been investigated. After the annealing under optimal conditions, the surface roughness of the InGaN structure reduces pronouncedly, accompanied by an improvement in the crystalline quality of the p-GaN cap layer, and an incorporation process of segregated In atoms into the p-InGaN layer occurs simultaneously and results in an increase of about 3% indium content. Furthermore, the annealing significantly improves the pn-junction behavior of the InGaN p-i-n structure by two orders of magnitude reduction in the reverse leakage current.

InGaN/GaN p-i-n Photodiodes Fabricated with Mg-Doped p-InGaN Layer

Mg-doped p-InGaN layers with In composition of about 10% are grown by metalorganic chemical vapor deposition (MOCVD). The effect of the annealing temperature on the p-type behavior of Mg-doped InGaN is studied. It is found that the hole concentration in p-InGaN increases with a rising annealing temperature in the range of 600–850°C, while the hole mobility remains nearly unchanged until the annealing temperature increases up to 750°C, after which it decreases. On the basis of conductive p-type InGaN growth, the p-In0.1Ga0.9N/i-In0.1Ga0.9N/n-GaN junction structure is grown and fabricated into photodiodes. The spectral responsivity of the InGaN/GaN p-i-n photodiodes shows that the peak responsivity at zero bias is in the wavelength range 350–400nm.

Characterization of Conduction Band Offset in Nanocrystalline TiO2/p-InGaN for Application to Water Photolysis Using Visible Light

We fabricate a rutile-rich TiO2 nanocrystalline layer by the sol–gel method on an epitaxial p-InGaN layer and characterize their conduction band offsets by photocurrent spectroscopy. The conduction band edge of p-In0.12Ga0.88N is higher in energy than that of the TiO2 nanocrystalline layer. The excitation of the TiO2/p-In0.12Ga0.88N electrode by 405 nm light causes a cathodic photocurrent and an increase in scattering light intensity owing to the hydrogen bubble formation on the electrode surface. These results indicate electron injection from the TiO2/p-InGaN electrode to the electrolyte and the possibility of hydrogen generation using visible light by TiO2/p-InGaN electrode.

Surface morphology control of green LEDs with p-InGaN layers grown by metalorganic chemical vapor deposition

The growth of green LEDs with In x Ga 1− x N:Mg p-type layers was studied by employing various epitaxial structures and substrates to control the surface morphology, especially in terms of the formation of pits. The pit densities of the green LED structures grown on sapphire substrates with p-type layers composed of a p-In 0.04Ga 0.96N:Mg and a graded p-In x Ga 1− x N:Mg are ∼1×10 9 and ∼3×10 8 cm −2, respectively. p-type layers composed of p-InGaN:Mg/p-GaN:Mg short-period superlattices are effective in preventing the formation of V-defect related pits. The pit density of green LED structures grown on free-standing GaN substrates with a p-In 0.04Ga 0.96N:Mg layer is ∼1.4×10 7 cm −2, which can be correlated to the threading dislocation density in the substrates.

High-Temperature Characteristics of AlxGa1-xN-Based Vertical Conducting Diodes

We investigated the high-temperature characteristics for AlxGa1-xN-based (x=0–0.57) vertical conducting diodes. In the forward current–voltage (I–V) characteristics, the offset voltage decreases with temperature because of the reduction of the built-in potential due to the decrease in the bandgap energy with temperature. In spite of an increase in SiC substrate resistance with temperature because of a decrease in the electron mobility, the on-state resistance of the diode with Al0.22Ga0.78N is as low as 1.45 mΩ cm2 even at 250 °C because of the reduced resistance of the p-InGaN layer due to an increase in the hole concentration. In the reverse I–V characteristics, the breakdown voltage increases with increasing Al composition, x, of AlxGa1-xN layer because the higher the Al composition of the AlxGa1-xN layer is, the higher the critical electric field becomes. Although the reverse leakage current of AlxGa1-xN-based diodes increases with increasing temperature, the breakdown voltage at elevated temperatures is similar to that at room temperature. These features indicate the feasibility of AlxGa1-xN-based diodes for high-temperature operation.

Control of quantum-confined Stark effect in InGaN∕GaN multiple quantum well active region by p-type layer for III-nitride-based visible light emitting diodes

We demonstrate the control of the quantum-confined Stark effect in InGaN∕GaN quantum wells (QWs), grown along the [0001] direction as part of the active region of visible light emitting diodes (LEDs). The effect can be altered by modifying the strain applied to the active region by the hole injection and contact layers. The optical characteristics and electrostatic potentials of the active region of the visible LEDs with different p-type layers are compared. LEDs with p-InGaN on top of the active region show a reduced blueshift in the peak wavelength with increasing injection current and a lower potential difference across the QW than those with p-GaN layers. The electrostatic potentials across the QW have estimated average values of ∼0.8 and ∼1.3MV∕cm for the active region of LEDs of current study with p-InGaN and p-GaN layers, respectively.

Nitride-Based Green Light-Emitting Diodes With Various p-Type Layers

The performance characteristics of green light-emitting diodes (LEDs) grown by metal-organic chemical-vapor deposition were investigated to study the dependence of the device performance on the materials and the growth conditions of p-type layer grown after the InGaN multiple-quantum-well active region. The electrical and structural qualities of Mg-doped p-In0.04Ga0.96N and p-GaN layers grown under different growth conditions were studied to optimize the growth conditions of p-type hole injection layers of green LEDs. A free-hole concentration of p=1.6times1018 cm-3 of with a resistivity of 0.33Omegamiddotcm was achieved for p-GaN:Mg layers grown at 1040degC. Lower hole concentrations and mobilities and rough surfaces were obtained when the growth temperature was decreased to 930degC in H2 ambient. In the case of p-In0.04Ga0.96N grown at 840degC in N2, a significant improvement of the hole concentration was achieved due to the reduced ionization activation energy of Mg acceptors in InGaN. Also we observed that as-grown p-GaN layers grown in N2 ambient showed p-type properties without Mg dopant activation. The electrical and optical properties of In0.25Ga0.75 N/GaN multiple-quantum-well green LEDs with such different p-layers were investigated. The electroluminescence intensity was improved for the LEDs with p-In0.04Ga0.96N layers grown at 840degC as compared to the LEDs with p-GaN layers grown at higher temperatures due to the reduced thermal damage to the active region, high hole injection, and low piezoelectric field induced in the active region. p-InGaN layers are very attractive candidates for the p-layer in green LED structures. The low temperature and N2 ambient used during the growth of InGaN layers are beneficial to protect the InGaN active region containing high-indium composition quantum-well layers in addition to the advantage of providing a higher hole concentration. However, the LEDs with p-In0.04Ga0.96 N layer showed a slightly higher turn on voltage which could originate from the potential barrier for hole transport at the interface of the p-InGaN layer and the last GaN quantum-well barrier. to reduce this problem, we designed and characterized an LED structure having a graded indium composition in the p-In0.04Ga0.96N layer in order to improve hole transport into the active region. Optimized LEDs with p-InGaN layers grown in a N2 ambient showed much brighter electroluminescence due to low damage to the active region during p-InGaN layer growth

Comparison of GaN and In0.04Ga0.96N p-Layers on the Electrical and Electroluminescence Properties of Green Light Emitting Diodes

We have compared the effects of Mg-doped GaN and In0.04Ga0.96N layers on the electrical and electroluminescence (EL) properties of the green light emitting diodes (LEDs). To investigate the effects of different p-layers on the LED performance, the diode active region structures were kept identical. For LEDs with p-InGaN layers, the p-In0.04Ga0.96N/GaN polarization-related EL peak was dominant at low current levels, while the multiple-quantum-well (MQW) peak became dominant at higher current levels, different from LEDs with p-GaN layers. Also, LEDs with p-InGaN exhibited slightly higher turn on voltages (V on ) and forward voltages (V f ) compared to LEDs with p-GaN layers. However, the MQW related EL intensity was much higher and diode series resistance lower for LEDs with p-InGaN layers compared with LEDs with p-GaN, showing possible improvements in output power for LEDs with p-InGaN layers. The diodes with p-GaN layers typically showed V f of ∼3.1 V at a drive current of 20 mA, with a series resistance of ∼24.7 Ω, while diodes with p-InGaN showed V f of ∼3.2 V, with a series resistance of ∼18.5 Ω, for device dimensions of 230 μm by 230 μm.