Wet Oxidation And High-power And High-efficiency 940 Nm Vertical Cavity Surface Emitting Laser Researc

Vertical cavity surface emitting lasers(VCSELs)have the advantages of the circular output beam,low threshold current,single longitudinal mode,high frequency modulation,high power,high efficiency,easy two-dimensional integration and low cost,which compared with the edge emission laser(EEL).VCSELs are widely used in 3D sensing,optical communications,consumer electronics,Internet of Things,lidar,and biomedicine.VCSELs offer high power density,high power conversion efficiency and high beam quality in these applications.According to the theory of tunnel junction tunneling,multi-junction VCSELs have outstanding advantages in power conversion efficiency,peak power,slope efficiency,and more friendly to drive and power supply.The multi-junction VCSEL array has multiple oxidation limiting layers,tunnel junctions and active regions.The thermal crosstalk between multi-junction VCSEL arrays is more severe than single-junction VCSEL arrays.It will increase the junction temperature,reduce output power and efficiency,and seriously affect device performance.In this paper,the thermal characteristics of 940 nm single-junction and multi-junction VCSEL arrays are simulated theoretically,fabricated,and packaged.The influences of mesas interval and oxidation aperture on the performance of VCSEL arrays are analyzed.The research content and innovation of this paper are as follows:1.The basic principle and structure design of single-junction and multi-junction VCSEL are introduced in detail.We analyze the threshold current,output power,conversion efficiency and thermal characteristics that affect VCSEL.In order to solve the problems of low efficiency and low power density of common VCSELs,a multi-oxide layer and multi-junction VCSEL is designed.We use COMSOL software to simulate the effect of oxidation aperture on the current density distribution of single-junction and multi-junction VCSEL.At the same injection current,five-junction VCSEL has higher current density and more uniform distribution than single-junction VCSEL,which helps improve power and efficiency.A three-dimensional thermal diffusion model is established based on COMSOL Multiphysics to simulate the temperature distribution and the thermal crosstalk of arrays from 2 μm to 6 μm mesa interval.The experimental results basically match with the simulation results,and the junction temperature deviation is less than 1.5 ℃.The optimal mesa interval of 6 μm is obtained by simulation,which reduces the junction temperature by 34.56% and increases the efficiency by 10.52% compared to2 μm mesa interval.It is verified that optimized mesa interval helps increase array efficiency and improve uniform temperature distribution,which facilitates higher power density and is more advantageous in terms of long-term reliability.2.We have systematically studied the wet oxidation process and mechanism.According to the Deal-Grove model,a mathematical model of oxidation depth with time is established.The simulated oxidation rate is 0.30 μm/min and the experimental oxidation rate is 0.28 μm/min,which is an important reference for precise control of oxidation aperture in experiments.We systematically study the laws of wet oxidation.The effects of different oxidation parameters on the oxidation rate and oxidation aperture morphology are investigated by experiment.Compared with other parameters,the effect of furnace temperature on oxidation rate is more obvious.Oxidation aperture morphology is mainly influenced by the pressure of the chamber.When other parameters are fixed,the higher the chamber pressure,the more the oxidation aperture tends to be round.This provides the theoretical and technical basis for precise control of the aperture size and morphology of different types of VCSELs.3.We introduce the VCSEL process in detail,focusing on the breakthrough of the key VCSEL preparation process and narrow pulse packaging and testing technology.We successfully solve the key process technology problems such as discoloration bulging of the ring electrode,precise control of low-damage ICP etching depth and angle,dielectric film and metal film adhesion and stress matching,and VCSEL sidewall chipping.4.Individual VCSEL with different oxidation aperture and VCSEL arrays with different mesa interval were prepared and packaged.High efficiency five-junction individual VCSEL is produced.For the five-junction individual VCSEL with the oxide aperture from 9 to 15 μm,the maximum power conversion efficiency is more than 60%,and the slope efficiency is more than 5.28 W/A under room temperature and pulse condition(50 μs pulse width,0.5% duty cycle).The optimal five-junction VCSEL array with oxidation aperture of 15 μm and mesa interval of 6 μm has the highest power conversion efficiency of 54.43%.In narrow pulse test(60 ns pulse width,0.0024% duty cycle),the peak power of five-junction array reached 517W@100 A.