Research Of The Theory And Key Technology For Fabrication Of The GaN-base Bule Violet Laser Diodes

GaN basedâ…¢-â…¤nitrides as a wide band gap semiconductor has played a key role in the research field of opoelectronic materials and devices, due to its promising appliciations and great potential market in LEDs,short-wavelength laser diodes,ultraviolet detectors, high temperature and high power electronic devices.Especially, GaN based bule-violet laser diodes with wavelength from 400 nm to 410 nm is the most promising light resource for high density storage system, therefore fabricating bule-violet short-weavelength laser is research focus of people.While for GaN base lasers, there are still some difficulties in growthing the related materials and fabricating devices, in particular,p-type GaN doping,crack-free thick AlGaN growth, high quality p-type ohmic contact.For exploring the above-mentioned problems, a series of studies were carried out on GaN base laser diodes, including simulation on one-dimension optical field, growth of related materials, investigation on low-resistance ohmic contact to p-GaN.The main contents were as followings:1) Through adopting transfer-matrix, one-dimension optical-field of GaN-base laser diodes was simulated, and the effect of each layer on GaN-base laser diodes was analysed. It was found that the thickness and Al component of n-typed AlGaN/GaN superlattice layer(SLS) should be increased in order to avoid the anti-waveguide behavior, If a thicker cladding couldn't be grown, approximate fundamental mode operation could be obtained by increasing the thickness of the GaN waveguide slightly.In the condition of good quality, the thinner the thickness of the n-type contact layer was, the smaller the optical confinement factor was. It is the first time to propose that through adopting InGaN or InGaN/GaN SLS as waveguide layer optical can be confined better, and lower threshold current density can be obtained.When the maximum optical confinement factor and the lowest threshold current density were chosen as object functions, the AlGaN/GaN/InGaN separate confinement heterojunction(SCH)MQW layer structure was optimized.When the thickness of the n-type contact layer GaN was assumed to be 2000nm, the p-type contact layer thickness is 200nm, which can be devided as follows: n-type cladding layer AlGaN/GaN SLS thickness is 600nm (120 pairs SLS), Al composition is 0.22; n-type waveguide layer thickness is 90nm, the number of the quantumwell of active layer is two; the p-type electron blocking layer AlGaN thickness is 10nm; p-type waveguide layer GaN thickness is 70nm;p-type cladding layer AlGaN/GaN SLS thickness is 300nm (60 pairs SLS), Al composition is 0.22.2) the effects of The TMA1 flow rate and growth temperature on AlGaN qualtity were investigated.We focused on how to obtain crack-free thick AlGaN material. In the thesis, AlGaN was substituted by AlGaN/GaN SLS, and free-crack thick cladding layer was obtained.3) The relationship between the emitting wavelength of InGaN/GaN MQW active region and the composition, the thickness of well and barrier was analyzed theoretically.It was found adjusting the composition and thickness of well and barrier properly, the wavelength needed can be obtained.In experiment, the active region was optimized through growthing LED structure.Through changing the well growth temperature, we found that the relationship between emitting wavelength and well temperature was a linear function, Thus, we can obtain special emitting weavelength through adjusting well temperature.Finally, we discussed the effect of changing well temperature on the optical character of InGaN/GaN MQW.4) The methods to obtain low ohmic contact to p-GaN was investigated.â‘ The surface treatment, annealing temperature and time and atmosphere of p-GaN were optimized.â‘¡Base on the above mentioned optimization condition, comparing Ni/Au contacting p-GaN with p-InGaN/p-GaN SLS as capping layer directy, we found that Ni/Au contact p-InGaN/p-GaN SLS can produce lower specific contact resistivity.When the temperature was chosen to be 550℃, the time of alloying in oxygen atmosphere was 30 minute, the lower specific contact resistivity(pc) was 1.99×10^-4Ωcm².â‘¢The reason of p-InGaN/p-GaN SLS forming low specific contact resistivity was investigated further.Firstly, the influence of temperature change of p-GaN in p-InGaN/p-GaN SLS on ohmic contact is discussed.It is found that the growth temperature of p-GaN in p-InGaN/p-GaN SLS increased, the contact resistance increased.Moreover, the effect of surface layer of capping p-InGaN/p-GaN superlattices on the contact to p-GaN was discussed. It was found that the specific contact resistance (pc) to p-type InGaN was lower when p-GaN was used as the surface layer.â‘£Using strained-balance theroy, substituteing p-InGaN/p-GaN SLS by p-InGaN/p-AlGaN SLS as p-GaN capping layer was proposed firstly, and lower specific contact resistivity was obtained. the value of P_c was 7.27×10^-5Ωcm² at room temperature.Furthermore, from the aspects of the band and the hole charge density, we analysed the reason of reduction on the contact resistance.Finally, we obtained low turn-on voltage and series resistance of InGaN-GaN LEDs using strained-compensated and strain-induced piezoelectric p-InGaN/p-AlGaN superlattice as contact layer.