Structure Design And Fabrication Of High Power Vertical Cavity Surface Emitting Laser

Comparing with the traditional edge emitting laser, vertical cavity surfaceemitting laser(VCSEL) shows many advantages, such as good beam quality, lowthreshold current, single longitudinal mode, easy fabrication in two-dimensionalarrays and low cost, and has been widely paid attention. In recent years, theenormous market of VCSEL in DPSS, medical treatment, optical communicationand other areas greatly promoted its research and development. People fabricatedVCSEL devices at different wavelength for different applications. In order to pumperbium fiber laser, the high power980nm device is fabricated. And high power laserat1060nm has wide applications in medical, industrial and military. In addition,green laser can be realized through intra-cavity frequency doubling, which is mainlyused in the market. At present, the research of VCSEL mainly focuses on the smallpower devices which are used in interconnection. This paper focuses on the structuredesign of1060nm VCSEL and the optimization of980nm VCSEL single and arraydevice.The active region and top and bottom DBR of1060nm VCSEL device arecalculated theretically and designed. In order to reduce the average strain of theInGaAs quntum wells, the GaAsP barriers which have the opposite strain of the welllayer are introduced into the active region. The bandgap, band offset and subbandenergy level of InGaAs/GaAsP QW are calculated, and the performance of VCSEL with different In component, number and thickness of QWs are compared. Then theparameters are defined: the active region is composed of threeIn_0.28Ga_0.72As/GaAs_0.8P_0.2 quantum wells, and the thicknesses of well and barrierlayers are9nm and15nm, respectively. The temperature characteristics of QWs withthree different barriers of GaAs, Al_0.15Ga_0.85As and GaAs_0.8P_0.2 are compared. Thematerial gain and output power of VCSEL with GaAs_0.8P_0.2 barriers show slowerdecreasing rates and better performance at high temperature compared with the othertwo barriers. The top and bottom DBR are composed of Al_0.1Ga_0.9As andAl_0.9Ga_0.1As with the thickness of quarter-wave, which have high and low refractiveindex respectively. The reflection spectra of DBR are calculated using transfermatrix method by considering the influence of dispersion, absorption loss and seriesresistance. The reflectivity of30pairs of P-DBR and20pairs of N-DBR are99.9%and99.3%, respectively. The overall structure of VCSEL is simulated using thesoftware of PICS3D. The center wavelength of output spectra is nearby1050nmconsidering the influence of temperature, which is agreed with the requirements.The structure of980nm VCSEL is optimized based on the design of1060nmVCSEL. The dependent of threshold current, output power and wall-plug efficiencyon the reflectivity of n-DBR is simulated theoretically, and the best reflectivity isobtained.980nm VCSEL single device and arrays are fabricated and the outputpower and spectra are tested. The peak output power of single device with anaperture of500μm is up to102W, corresponding to a power density of52kW/cm2,when the injection current is110A, which is greatly improved compared withdevices before optimization. The peak power of4*4and5*5arrays is98W and103W at100A. The P-I characteristics and the spectra of the single device arecompared at different injection currents under CW, quasi-CW, and pulsed operation,respectively. The inner temperature rise of device caused by self-heating effectmakes the output power saturated soon. It is concluded that the red shift rate of thelasing wavelength is0.92nm/A and0.3nm/A under CW and QCW operation,respectively. And it is only0.0167nm/A under pulsed operation, which is far less than that under the other two conditions.The heat transport model of VCSEL array is established and simulated using theComsol Multiphysics software. The trend of temperature rise is obtained bychanging the cell diameter and gap between the adjacent cells in array. It isconcluded that the cell diameter should be smaller than150um and the best values isfrom50um to100um in order to reduce the temperature rise and the size of array andimprove the density of output power. Three kinds of arrays are manufactured andtested:4*4,5*5and8*8. The power are580mW,1440mW and2100mW, thecorresponding power density are115W/cm²,374W/cm², and853W/cm². The valuesof temperature rise at4A are120℃,58℃, and38℃, which are obtainedby redshiftof wavelength. The results of simulation are in good agreement with experiment.8*8and10*30arrays with the cell diameter of100um are fabricated, the output powerunder CW operation reaches to2.73W and5.26W, respectively.