The Design Of The Epitaxial Structure Of GaN-based Green Laser Diode And The Research On Photoelectric Performance

GaN based green laser diodes have made great progress in photoelectric performances in recent years,and it has important applications in laser printing,laser measurement,laser display,laser lighting and communication.Although some progress has been made in photoelectric performances and applications,there are still some key scientific problems,such as low injection efficiency,strong polarization effect,serious photon leakage,low electro-optical conversion efficiency and so on,which affect the photoelectric performances of laser diodes.The results show that electron leakage is serious and hole injection efficiency is low.It is important to reduce electron leakage,improve injection efficiency and optical limiting factors for improving the photoelectric performances.In this paper,we studied quantum well layer,waveguide layer and electron blocking layer and the relationships among their photoelectric performances.Based on the above study,the optoelectronic performances of the device are improved by designed epitaxial structure.The contents and results mainly include the following:（1）The effect of the number of quantum well on the photoelectric properties of green laser diodes was studied using the k·p method.The results show that electron injection efficiency increased and the carrier concentration in active region decreased resulting in reducing Auger recombination,when the number of quantum well period increased from 1to 3.When the number of quantum well periods is 3,the output power is 234.95 m W,and the electro-optical conversion efficiency is 7.8%.When the number of quantum well continues to increase,the band bending and carrier leakage are serious due to the accumulation effect of polarization field,which leads to the decrease of device performance.At the same time,the consumptions of raw material and difficulty increase in growing high quality epitaxial materials with the number of quantum well increasing.（2）The optical field distribution of GaN based green laser diode depends on waveguide structure which has an important effect on photon loss and electrical properties of the devices.Waveguide structure of GaN based green laser diode were designed as single waveguide and dual-waveguide structures.The results show that asymmetric dual-waveguide can limit light field distributed in the active and waveguide regions and keep light field away from p type zone,which can reduce photon absorption loss.Moreover,it can reduce the resistance of the epitaxial layer and the threshold current decreases to116.9 m A.The output power of the device increases to 227.5 m W and the electro-optical conversion efficiency increases to 7.2%.Hence,the optoelectronic performance of asymmetric dual-waveguide structure GaN based green laser diodes is better than that of single waveguide structure.（3）On the basis of designed asymmetric dual-waveguide structure,the effect of indium content in n-In_xGa_1-xN waveguide layer on its photoelectric performance was discussed.The refractive index difference between the n-cladding layer and the waveguide layer and the optical field distribution in the epitaxial layer were improved by regulating the indium content in n-In_xGa_1-xN waveguide layer,which makes optical field offset in order to reduce the photon loss.Meanwhile,band gap of the waveguide layer was controlled by changing indium content in waveguide layer,which can not only reduce the barrier of hole injection,but also improve the barrier of electron leakage.When the indium content of waveguide layer is 0.07,internal quantum efficiency reaches 80%,output power of the laser increased to 234.95 m W,and electric-to-optical conversion efficiency reaches 7.8%.（4）Electronic leakage is one of the key problems of quantum inefficiency in GaN based laser diode.A quaternary In Al GaN electronic block layer structure can reduce the valence band offset so that hole injection efficiency is improved.The results indicated internal quantum efficiency increased and high power and high electro-optic conversion efficiency were achieved.The photoelectric performances of GaN based green laser diode are improved by designing and adjusting the aluminum composition of electronic block layer.The results show that the stepped linear aluminum content graded electronic block layer can effectively reduce working voltage and increase optical output power.So electric-to-optical conversion efficiency reaches 8.3%.Band structure simulation results show that step linear Al content graded electron block layer significantly reduces hole injection band offset.It can improve carrier concentration distribution in multiple quantum wells,which can reduce non-radiative recombination current density and internal quantum efficiency.