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Key Fabrication Technologies For Semi-polar Algan-based Ultraviolet Light-emitting Diode

Posted on:2019-02-22Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q DaiFull Text:PDF
GTID:1368330590975118Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
In recent years,there has been an outburst of the research on the AlGaN-based ultraviolet light emitting diodes?UV-LEDs?that have great potential in many application areas,such as sterilization,air and water purification,and resin/ink hardening.However,the IQE of the polar AlGaN-based UV-LEDs has been seriously restricted due to the quantum confined Stark effect?QCSE?induced by the spontaneous and piezoelectric polarization fields along the polar[0001]c-direction.In contrast,the direction of the polarization fields for the semi-polar AlGaN-based UV-LEDs is titled with the growth direction,resulting in an effective suppression of QCSE.As a result,superior performance is expected for the semi-polar?11???2?plane AlGaN-based UV-LEDs to their polar counterparts.Therefore,it is vital to conduct systematic researches on the?11???2?plane AlGaN materials.In this dissertation,the epitaxial growth of?11???2?plane AlGaN materials on the non-polar?10???0?m-plane sapphire substrates in low-pressure metalorganic chemical vapor deposition?LP-MOCVD?system were investigated extensively.And the researches on the key fabrication technologies for?11???2?plane AlGaN-based UV-LED,such as the Si doping of semi-polar AlGaN epi-layers,the growth of semi-polar AlGaN multiple quantum wells?MQWs?,and the Mg doping of semi-polar AlGaN epi-layers were also performed.The contents and major results achieved in this research were listed as follows:1.The semi-polar?11???2?plane AlGaN films were grown on the non-polar?10???0?m-plane sapphire substrates with MOCVD system.And the infulences of the growth conditions,such as layer structure,nitridation time,and reactor pressure,on the properties for the semi-polar?11???2?plane AlGaN epi-layers were studied systematically.And the?11???2?plane AlGaN films with good surface morphology,high crystalline quality and low background electron concentration were obtained.Meanwhile,the?11???2?plane AlxGa1-xN films with the Al composition varied in the range of 0.08-0.66 were achieved and the structural and optical properties for the?11???2?plane AlxGa1-xN films were characterized.It was revealed that surface roughness values for the as-deposited semi-polar?11???2?plane AlxGa1-xN films were decreased continuously as the Al composition was increased.In contrast,the crystalline quality for the?11???2?plane AlxGa1-xN films was degraded with increasing the Al content.2.The semi-polar?11???2?plane Al0.45Ga0.55N epi-layers with various Si-doping levels were successfully deposited and the influences of Si-doping on the characteristics of?11???2?plane Al0.45Ga0.55N flims were investigated.The characterization results showed that the compressive strain in the as-deposited Al0.45Ga 0.55N epi-layers could be completely relaxed by Si-doping with appropriate SiH4 mole flow rate owing to the enhanced dislocation movements induced by Si dopants.This fact implies that Si-doping to the semi-polar?11???2?plane Al0.45Ga0.55N epi-layer is especially beneficial to the interaction and annihilation of the dislocations,resulting in a significant improvement in crystalline quality.Moreover,an electron concentration as high as 1.93×1019 cm-3 was achieved when the SiH4 mole flow rate was 8.93nmol/min.3.semi-polar?11???2?plane AlGaN-based multiple quantum wells?MQWs?with an emission wavelength of 279 nm were successfully deposited and the effects of indium?In?surfactant on the properties of the AlGaN-based MQWs were investigated intensively.The characterization results revealed that the surface morphology as well as the crystalline quality for the semi-polar?11???2?plane AlGaN MQWs could be improved remarkably by adopting In as surfactant during the MOCVD growth process.Furthermore,the integrated MQWs-related excition emission peak intensity and the radiative recombination probabilities in MQWs could be increased as well with the help of In-surfactant,resulting in an improved exciton localization energy and an enhanced IQE.4.The Mg-delta-doped semi-polar?11???2?plane Al0.15Ga0.85N films were successfully deposited and the effects of Cp2Mg mole flow rate on the characteristics of the p-AlGaN films were investigated intensively and systematically.The measurement results indicated that the crystalline quality of the semi-polar?11???2?plane p-AlGaN films could be improved to a certain extent by optimizing the Mg-delta-doping process as a result of the suppression of the dislocation propagation along the growth direction.Furthermore,a hole concentration as high as 5.4?10177 cm-3 were achieved at room temperature by optimizing the Cp2Mg mole flow rate.In addition,the rapid thermal annealing?RTA?technique for the?11???2?plane p-Al0.15Ga0.85N epi-layers was optimized.It was found that the hole concentration for the?11???2?plane p-Al0.15Ga0.85N films could be further improved to 7.9×10177 cm-3 with multiple-step RTA technique in various gas ambient.5.The non-polar?11???0?a-plane AlGaN-based UV-LEDs with various kinds of electron blocking layers?EBLs?were analyzed numerically with the APSYS simulation software.The simulation results revealed that the a-plane AlGaN-based UV-LED with the Al0.634In0.03Ga0.336N/Al0.5Ga0.5N superlattice?SL?EBL displays obviously superior characteristics in reducing electron leakage and enhancing hole injection efficiency as compared to the traditional EBL,resulting in the enhancement of radiative recombination in the active region and the improvement in the efficiency droop at high injection current density.
Keywords/Search Tags:AlGaN-based UV-LEDs, semi-polar(11(?)2) plane, metalorganic chemical vapor deposition(MOCVD), Si-doping, Mg-doping, AlGaN-based multiple quantum wells(MQWs), non-polar AlInGaN-based electron blocking layer(EBL)
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