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Research On Growth And Photoelectric Properties Of AlInGaN Multiple Quantum Wells Luminescent Metarials

Posted on:2016-04-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:T LiuFull Text:PDF
GTID:1108330479478733Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
Quaternary AlxInyGa1-x-yN alloys semiconductor could independently modulate the band gap and lattice constant by adjusting the composition of Al and In. The carrier confinement effect can be enhanced by using Al In Ga N as barrier layers of quantum wells, which is similar to Al Ga N. The carrier localization effect and radiative recombination efficiency can be increased by using Al In Ga N as well layers of quantum wells, because of the characteristic of insensitivity to the dislocation. Therefore, Quaternary AlxInyGa1-x-yN alloys have attracted much attention and become the most potential material of efficient light-emitting diodes(LEDs). However, the issues about the composition of the quaternary AlxInyGa1-x-yN alloys and the lattice match are still not resolved. In this dissertation, the multiple quantum wells(MQWs) with Al In Ga N have been deposited by metalorganic chemical vapor deposition(MOCVD) technology. The Al In Ga N has been grown as well or barrier layers by adjusting the Al composition by varying the flow rate of Al precursor. The blue and near-ultraviolet(UV) MQWs are grown, which are lattice-matched with Ga N substrate. The recombination mechanism of carrier in the MQWs with increasing temperature has been proposed according to the optical properties of the samples. The LEDs chip has also been prepared. The details are as follows:Three blue In0.20Ga0.80N/AlxInyGa1-x-yN MQWs samples with wavelength of around 450nm(1#-3#) and three near-UV In0.08Ga0.92N/AlxInyGa1-x-yN MQWs samples with wavelength of around 390nm(4#-6#) have been grown on c-plane sapphire substrate with MOCVD equipment. The varying Al composition can be obtained by adjusting the flow rate of Al precursor during the the growth process of Al In Ga N barrier layers. The issues about the lattice match between Al In Ga N barrier layer and Ga N substrate have been discussed. In addition, one near-UV Al0.11In0.13Ga0.76N/Al0.16In0.045Ga0.795 N MQWs sample has been grown by using Al In Ga N as well layers(7#).The structure and interface quality of the samples have been investigated by means of high-resolution X-ray rocking curves. The composition has been estimated according to the positions of the diffraction peaks. The influence of the flow rate of Al precursor on the composition has been analyzed. The Al composition of AlxInyGa1-x-yN barrier layers increase and In composition decrease with increasing the flow rate of Al precursor, indicating that the increase of the flow rate of Al precursor has suppressed the In composition. The lattice mismatch between well and barrier layers or barrier layers and Ga N substrate has been calculated by using the composition.Atomic force microscopy(AFM) was utilized to study the surface morphology. Many V-shaped pits can be observed. The density of the dislocation pits decreased with reducing the lattice mismatch degree between Al In Ga N barrier layers and Ga N substrate, indicating that the pits generated at the interfaces between barrier layers and Ga N substrate. The root-mean-square roughness increases with increasing Al composition of barrier layers, due to the three-dimensional island-like growth mode enhanced by increasing the Al composition.Raman measurements were carried out at room temperature to verify the existence of In-rich clusters. The vibration modes can be clearly seen which corresponding to the A1(TO) of the In N and A1(TO) and E2(high) of Al N. The intensity of the Raman vibration increase with increasing the composition, indicating that In-rich and Al-rich clusters exist in the samples. The compositional fluctuation can be formed in the energy band.Room temperature photoluminescence(PL) measurement was performed to investigate the optical properties of the samples. In blue and near-UV MQWs samples, PL emission peak energies exhibit redshift with increasing Al content in barrier layers, which is induced by the increase of quantum-confined Stark effect(QCSE). The clear S-shaped behavior can be easily observed from the PL emission peak energy as a function of temperature, indicating the existence of carrier localization effect. The emission energies are fitted by the Varshni equation and divided into three temperature intervals. The transition temperature occurs at higher temperature with increasing the Al composition. The carrier localization degrees are calculated by the equation. In two series of samples, the carrier localization effect becomes stronger in the samples(3# and 5#) which achieved lattice-matched.The multi-Gaussian type distribution functions are carried out to fit the experimental data of the temperature-dependent PL spectra in sample 3#. The band edge and localized states emission can be obtained. The integrated intensity ratio of localized states to band edge emission Ilocalized/IBE and the emission peak energy of localized states increase from 10 K to 160 K, and then decrease with further increasing the temperature. The possible recombination mechanism of carriers in the QWs with increasing temperature was proposed and devided into four stages.The PL intensity and full width at half maximum(FWHM) could be remarkably enhanced by substituting quaternary Al In Ga N for In0.08Ga0.92 N as the well layers. The carrier localization effect will be improved significantly by using Al In Ga N as well layers due to the increase in the local potential fluctuation.Blue In0.20Ga0.80N/Al0.16In0.027Ga0.813 N LED chip is prepared by standard chip fabrication process. Turn-on voltage is calculated by measuring the I-V curve of the LED chip, indicating larger equivalent resistance. The optical output power is 70.5m W when the current is 20 m A. The luminous efficiency reaches the maximum value when the current is 9m A and then gradually decreases. The wavelength of electroluminescence(EL) peak decreases exponentially. It is estimated that the wavelength will reach a stable value when the current is 30 m A. The FWHM of EL emission peaks decrease sharply and then gradually decreases with increasing the current, indicating the large number of localized states in the LED chip. The external quantum efficiency is 1.36% and color purity is 93.9% when the current is 20 m A, indicating the good optical properties.
Keywords/Search Tags:AlInGaN, MOCVD, LED, multiple quantum wells, lattice matching, localization effect
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