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Three kinds of electron-blocking layer(EBL) AlGaN based LED were compared numerically.They are conventional AlGaN EBL,AlGaN-GaN-AlGaN(AGA) and gradual Al composition AlGaN-GaN-AlGaN(GAGA) EBL.Their porfermance were analyzed involved carrier concentration in the active region,energy band diagram,electrostatic field and internal quantum efficiency(IQE).The results indicate that the LED with an GAGA EBL exhibits a better hole injection efficiency,a more peaceable efficiency droop,a lower electron leakage,and a smaller electrostatic field than the LED with a conventional AlGaN EBL or with an AGA EBL.

In order to realize preferable white light-emitting diodes with high color rendering index and optimized luminous efficiency,white InGaN/GaN multi-quantum-well dual-wavelength light-emitting diodes(LEDs) were grown on(0001)-oriented sapphire substrates by metal-organic chemical vapor deposition(MOCVD).Photoluminescence and electroluminescence properties of dual-wavelength LEDs with different In content were also studied.The experimental results indicated that In component plays a critical role on stability for electroluminescence spectrum and luminous efficiency of the dual-wavelength LED structures.In addition,YAG∶Ce phosphor-converted white light emission with high color rendering index was achieved using dual-blue emitting active regions.

The influence of Si doping on the photoluminescence (PL) properties of (Al"0"."3Ga"0"."7)"0"."5In"0"."5P/Ga"0"."5In"0"."5P multiple-quantum-wells (MQWs) was studied. For the samples without p-type layers, the PL peak wavelength from (Al"0"."3Ga"0"."7)"0"."5In"0"."5P/Ga"0"."5In"0"."5P MQWs did not vary when Si was doped in MQWs, the PL peak intensity did not change obviously and the PL FWHM broadened. We consider that Si doping results in worse interface quality of (Al"0"."3Ga"0"."7)"0"."5In"0"."5P/Ga"0"."5In"0"."5P MQWs. However, for the full light-emitting diode (LED) structure samples, the PL intensity of MQWs obviously increased when Si was doped in MQWs. The PL intensity from MQWs with Si-doped barriers was about 13 times stronger than that of undoped MQWs. The PL intensity from MQWs with Si-doped barriers and wells was strong as 28 times as that of undoped MQWs. The reasons are discussed.

AlGaInP/GaInP multiple quantum well structures were grown by low-pressure MOCVD on n-GaAs substrates. The influence of Si-doping to the characteristics of AlGaInP/GaInP multiple quantum wells was studied. The PL intensity from MQW with Si-doped barriers is about 13 times stronger than that of undoped MQW. The PL intensity from MQW with Si-doped barriers and wells is strong as 28 times as that of undoped MQW.

The characteristics of nitride-based blue light-emitting diodes (LEDs) with AlGaN composition-graded barriers are analyzed numerically. The carrier concentrations in the quantum wells (QWs), the energy band diagrams, the electrostatic fields, and the light output power are investigated by APSYS software. The simulation results show that the LED with AlGaN composition-graded barriers has a better performance than its AlGaN/InGaN counterpart owing to the increase of hole injection and the enhancement of electron confinement. The simulation results also suggest that the output power is enhanced significantly and the efficiency droop is markedly improved when the AlGaN barriers are replaced by AlGaN composition-graded barriers.

The energy band properties, density of states, and band alignment of the BexZn1−xO1−ySy alloy (Be- and S-doped wurtzite ZnO) are investigated by the first-principles method. BexZn1−xO1−ySy alloy is a direct band gap semiconductor, the valence band maximum (VBM) and the conduction band minimum (CBM) of BexZn1−xO1−ySy are dominated by S 3p and Zn 4s states, respectively. The band gap and lattice constant of BexZn1−xO1−ySy alloy can be modulated by changing the doped content values x and y. With the increase in Be content value x in the BexZn1−xO1−ySy alloy, the band gap increases and the lattice constant reduces, but the situation is just the opposite when increasing the S content value y in the BexZn1−xO1−ySy alloy. Because the lattice constant of Be0.375Zn0.625O0.75S0.25 alloy is well matched with that of ZnO and its energy gap is large compared with that of ZnO, so the Be0.375Zn0.625O0.75S0.25 alloy is suitable for serving as the blocking material for a high-quality ZnO-based device.

The optimized structure parameters, electron density of states, energy band structures and optical bandgaps of the TM0.125Zn0.875O (TM=Be, Mg) alloys and Ga-doped TM0.125Zn0.875O are calculated and analyzed by using the ultra-soft pseudopotential approach of the plane-wave based upon density functional theory. The theoretical results show the Ga-doped TM0.125Zn0.875O materials are easily obtained and their structures are more stable. The Ga-doped TM0.125Zn0.875O are good n-type materials and their energy bandgaps are determined by Ga 4s states of the conduction band minimum and O 2p states of the valence band maximum. Compared with the TM0.125Zn0.875O alloys, the optical bandgaps of Ga-doped TM0.125Zn0.875O become wider due to the Burstein-Moss shift and many-body effects, which is consistent with previous experimental data. The Ga-doped TM0.125Zn0.875O materials are suitable as TCO films for the UV and deep UV optoelectronic device.

Dual-wavelength LEDs with doped quantum well barriers of different doping concentrations are numerically investigated by using the APSYS simulation software. The carrier concentrations, radiative recombination rates, energy band diagrams and spectra are investigated at different doping types and different doping concentrations. The results show that through adjusting the doping concentration of the quantum well barrier a suitable spectrum can be obtained, which will satisfy the need of application. And the effect of spectrum-control in dual-wavelength LED is due to the blocking effect of electrons and holes by doped quantum well barriers.

Optical properties of GaN-based light-emitting diodes (LEDs) are studied numerically by using AlGaN and InAlN electron-blocking layers (EBLs). Through the simulations of emission spectra, carrier concentration distribution, energy band, electrostatic field, internal quantum efficiency and output power, the results show that the LEDs with design of the InAlN EBL structure have a better performance over the original LEDs using an AlGaN EBL. The spectrum intensity and output power are enhanced significantly, and the efficiency droop of internal quantum efficiency is improved effectively with this design of InAlN EBL structure. It is proved that the strengths of carrier confinement and electron leakage current play a critical role in the performance of luminescence in LEDs.

A two-dimensional simulation of electrical and optical characteristics of dual-wavelength LED (light-emitting diode) with doped GaN interval layer is conducted with software.It shows that by the use of doped GaN interval layer, we can solve the luminescence intensity disparity of the two kinds of quantum wells in dual-wavelength LED. And through control of the thickness of the interval layer, we can adjust the relative luminescence intensity of the two kinds of quantum wells. Therefore, the effect of spectrum-control in dual-wavelength LED is due to the blocking effect of holes or electrons by doped GaN interval layer.

The growth of GaP layer on GaN with and without buffer layers by metal-organic chemical vapour deposition (MOCVD) has been studied. Results indicate that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature (HT) GaP growth. These sites can promote the two-dimensional (2D) growth of HT GaP and reduce the surface roughness. A GaP single crystal layer grown at 680 °C is obtained using a 40-nm thick GaP buffer layer. The full-width at half-maximum (FWHM) of the (111) plane of GaP layer, measured by DCXRD, is 560 arcsec. The GaP layer grown on GaN without low temperature GaP buffer layer shows a rougher surface. However, the FWHM of the (111) plane is 408 arcsec, which is the indication of better crystal quality for the GaP layer grown on GaN without a low temperature buffer layer. Because it provides less nucleation sites grown at high growth temperature, the three-dimensional (3D) growth is prolonged. The crystalline quality of GaP is lightly improved when the surface of GaN substrate is pretreated by PH3, while it turned to be polycrystalline when the substrate is pretreated by TEGa.

This paper reports that highly transparent and low resistance tantalum-doped indium tin oxide (Ta-doped ITO) films contacted to p-type GaN have been prepared by the electron-beam evaporation technique. The Ta-doped ITO contacts become Ohmic with a specific contact resistance of ~ 5.65 × 10−5 Ωcm2 and show the transmittance of ~98% at a wavelength of 440 nm when annealed at 500 °C. Blue light emitting diodes (LEDs) fabricated with Ta-doped ITO p-type Ohmic contact layers give a forward-bias voltage of 3.21 V at an injection current of 20 mA. It further shows that the output power of LEDs with Ta-doped ITO contacts is enhanced 62% at 20 mA in comparison with that of LEDs with conventional Ni/Au contacts.

We report an efficient white-light emission based on a single copolymer/InGaN hybrid light-emitting diode. The single copolymer consists of a conjugated polyfluorene backbone by incorporating 2,1,3-benzothiadiazole (BT) and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (DBT) as green and red light-emitting units, respectively. For the single copolymer/InGaN hybrid device, the Commission Internationale de l'Eclairage (CIE) coordinates, color temperature Tc and color rendering index Ra at 20mA are (0.323,0.329), 5960K and 86, respectively. In comparison with the performance of red copolymer PFO-DBT15 (DOF:DBT = 85:15 with DOF being 9'9-dioctylfluorene) and green copolymer PFO-BT35 (DOF:BT = 65:35) blend/InGaN hybrid white devices, it is concluded that the chemically doped copolymer hybridized device shows a higher emission intensity and spectral stability at a high driving current than the polymer blend.