| The vertical cavity surface emitting semiconductor laser is a new type of light source with compact structure and excelent performance.It can realize the laser emission on the surface of the chip,has the advantages of small threshold current,easy two-dimensional integration and circular symmetrical spot,and has quickly become a research hotspot.However,in terms of the current spreading of the conventional VCSEL,the metal electrode has a good current spreading property,but it has a strong absorption of the emitted light,so the conventional VCSEL relies on the top heavily doped layer for current spreading.However,there is still a disadvantage that the top heavily doped layer not only has poor current spreading performance,but also absorbs part of the emitted light,which reduces the light output power of the device.Therefore,a transparent conductive oxide(TCO)film having excelent photoelectric performance can solve the above-described current spreading problem.Based on the above research background,this paper designed a vertical cavity surface emitting laser with aluminum oxide aluminum(AZO)film as transparent electrode for the problem of uneven current injection and increasing output power of vertical cavity surface emitting laser.The main research work is as follows:1 A comparative analysis of various film preparation techniques was carried out,and finally the atomic layer deposition(ALD)technique was selected which not only has a low growth temperature but also has a unique advantage such as uniform thickness,precise controllability,and good shape retention.The preparation process parameters of AZO transparent conductive film are designed,including the cycle ratio of Zn:Al,deposition temperature and thickness of the AZO film.Then,the AZO film was prepared on gallium arsenide(GaAs)substrate and glass substrate by ALD technique,respectively.The electrical and optical properties of the AZO film were studied using relevant testing methods.2 First,testing the reflectivity of the AZO film.The results show that the reflectivity of AZO film is basical the lowest at 850 nm wavelength,which is in line with design expectations.Then,conducting the corrosion test of the AZO film.The results show that ammonia water: deionized water = 1:10 ratio of corrosive liquid,corrosion rate is slow,can be controlled,suitable for the corrosion process of AZO transparent conductive film.Furthermore,annealed experiment of the AZO transparent conductive film by RTP rapid annealing furnace.Studied the effects of annealing temperature on the surface morphology,electrical resistivity and transmittance of the AZO film.The results show that the surface roughness of the AZO film deposited on the GaAs substrate decreases with the increase of the temperature after the retreat,and the root mean square roughness decreases from 3.56 nm before annealing to 2.22nm(annealing at 500°C);The resistivity of the film increases first and then decreases with the increase of temperature.The contact characteristics of AZO film with metal show that the contact characteristics are best under annealing at 420°C;the transmission of AZO film after annealing at 850 nm The rate is slightly reduced,but still has a high transmittance of about 90%.The above test results are important for the introduction of AZO thin films into transparent GaAs-based VCSEL devices as transparent electrodes to improve the performance of VCSELs.3 The AZO transparent electrode VCSEL device was simulated and simulated.Calculated the current distribution and current-voltage characteristics when introduced the AZO transparent conductive film into VCSEL device.The results show that after introduced the AZO transparent conductive film into the VCSEL device,its the current injection condition is much more uniform than that of the conventional VCSEL device.Under the same current injection condition,the operating voltage of the AZO transparent electrode VCSEL is lower than that of the conventional VCSEL device.At the same time,designing the preparation process of VCSEL device with AZO transparent conductive film.Two sets of 850 nm VCSEL devices were successfully fabricated,which are VCSEL devices with AZO transparent electrodes and VCSEL devices without AZO transparent electrodes.Comparing the performance of two sets of VCSEL devices.The results show that the output power of conventional VCSEL and AZO-VCSEL devices is 2.01 mW and 2.57 mW at 9mA injection current,respectively.The output power of AZO-VCSEL devices is improved compared to conventional VCSEL devices.At 4mA injection current,the operating voltages of conventional VCSEL and AZO-VCSEL devices were 3.93 V and 3.53 V,respectively,indicating that VCSEL devices incorporating AZO transparent electrodes have lower contact resistance.That is consistent with the simulation results. |
