The Research About The Noise For The Reliability Of High Power Semiconductor Laser And Bipolar Transistor

widely used in optical fiber communication, optical sensor, informationmemory, medical treatment, pumping solid lasers and optical fiberamplification. The quality and reliability of semiconductor lasers isimperative in all the applications. At present, the usual method of screen iselectric aging by increasing the temperature and aging current to measureLDs threshold, quantum efficiency and output power. The result of aging isstatistic, and the time is long, and the method is not sensitive for potentialdefects. During the aging, the lifetime of the reliable devices is also affected.Thus, it is significant to find a kind of a fast, nondestructive, convenientmethod to test the devices and estimate their reliability. The electric noise insemiconductor devices, which reflects the quality and reliability of device,can be used to detect the reliability of device. At present, this method isapplied in bipolar transistor, Zener diode, GaAs MESFET. In recent years,we research the relation between noise and the quality and reliability ofsemiconductor laser.In this paper, it's summarized that the math basis of noise and thevariety,characteristics and producing mechanism. It's given that the noisetest method and test system used in experiment. Based on the theory andtest system, we research the electric noise of semiconductor lasers afterannealing and the relation between the change of electric noisecharacteristic and the reliability of device. It's also discussed that therelation between electric noise and technics of bipolar transistor.1.Improved on the test instrument, lowered the background noiseeffectively and increased the test veracity. The background noise should below enough since the noise of semiconductor laser is very weak. We adoptthe direct measure and cross-spectrum measure technology, which lower thebackground noise of system. The noise before and after cross-spectrum are1nV/Hz1/2 and 0.1nV/Hz1/2 respectively. The samples are screened triply tocontrol the external disturbing,and the multi-grounding is adopted to avoidelectromagnetic disturbing. The direct current power supply isn't fit for thenoise test because the fluctuation of output current will reflect the noise ofdevice. We adopt large capacity battery(continuously work 7h at 1A)which can fulfill big output current and low noise to avoid disturbing。2. It's discovered that annealing effect is produced in semiconductorlaser at some aging current, and the reason was discussed. The devices usedin the experiment are 808nm GaAs/GaAlAs semiconductor lasers. Attemperature (18±2) ℃, the electric derivative and the low frequencyelectric noise of devices are measured. The test processes are repeated afteraging test at 0.5A. It's found that the electric derivative curve of somedevice turned to be bad, but the noise frequency spectrum density decreased.Generally, the initial noise of good device is lower and change little afteraging, and the initial noise of bad device is higher and increase obviouslyafter aging. In the experiment, we found that the noise of bad devicedecreased by contraries 。 That's because the structure of 808nm isGaAs/GaAlAs, and there exists REDR(Recombination Enhanced DefectReactions)effect which make the defect acquire power and quicken themovement in Ⅲ-Ⅴmaterial. Moreover, some defects are annealed tostable state for the aging condition that the temperature(18±2)℃and 0.5Aaging current is the annealing process for devices. Though the noise ofdevices decrease, the quality of devices still fail. That's because the initialdefects producing at high temperature still exist. The research illuminates:The annealing effect will appear at some aging current. The noise of baddevices decreases after aging. By comparing the initial noise and the declinerate after aging can eliminate the failed products. The results are importantfor learning the characteristic of noise and correct the noise test criterion。3. It's found that g-r noise and burst noise produced in semiconductorlasers at accelerated aging condition maybe the symbol of the degenerationof the device. The reason of g-r noise and burst noise are also analyzed andit's pointed that they are produced by the same kind of defect source. Inexperiment, the noise of 808nm GaAs/GaAlAs high power quantumsemiconductor laser is measured. The noise frequency spectrum densitiesbefore and after aging are measured at 20uA firstly. Then the devices areaged at 0.5A,0.7A,0.9A respectively and the measurements are repeatedafter aging . It's found that there exist g-r noise and burst noise at 0.7A and0.9A, but there are no g-r noise and burst noise at 0.5A and before aging.That's because new defects , generate-recombination centers andShockley-Read-Hall (SRH) center are produced for the increase of agingcurrent, and parts of defects will move to space charge area,which produceg-r noise and burst noise. The result illuminate:The g-r noise and burstnoise of 808nm high power quantum semiconductor lasers have relationwith aging current. If the aging current is higher than a certain number, thenew defects will be induced in p-n junction and the g-r noise and burst noisewill be induced too. The g-r noise and burst noise may be the symbol offailed device and come from the same defect source.4. Used wavelet on the estimate and analysis of semiconductor lasersby testing noise, which offers a new method of estimate and filtering onsemiconductor laser. Wavelet is used to analyze the noise signal andestimate the reliability in semiconductor. Wavelet can analyze the signal inthe time and frequency domain at the same time, and can efficientlydifferentiate between the break section and noise. Thus, 1/f component ofnoise signal in the semiconductor laser can be extracted, and the 1/f noisereflects the imperfects of material or device, which is related with thequality of the device. Using the time-frequency localization of the wavelet,the curve of the time domain of the noise can be analyzed by themulti-resolution analysis, so that we can efficiently analyze theinstantaneous change and estimate the quality of the device. It is a newmethod to estimate the reliability of the device.5.Researched the relation of electric noise of bipolar transistor and leakcurrent, pointed that lowering leak current is the effective method oflowering electric noise and adopting cover structure terminal technique canlower electric noise effectively. At temperature(22±2)℃, three kinds ofNPN bipolar transistor samples(2688B,2688S,2688,each 15 只)aremeasured. The samples adopt three kinds of terminal technology. They are2688B table-board structure, 2688S semi-insulated multi-crystal Si structureand 2688 terminal overlay structure. The direct parameters of three kinds ofsamples are measured firstly, it's found that the leak current Icbo of 2688 areleast, and the Icbo of 2688S,2688B are higher. Then the noise of three kindsof samples are measured, it's found that the samples with higher Icbo alsohave higher noise. That's because the noise of transistor has direct relationwith interface leak current, and the terminal technology adopted by 2688control movable carrier and lower the leak current of transistor effectively,thus lower the noise of transistor. The research results show that theterminal technology can control the leak current of transistor and lower thenoise, thus increase the reliability of transistor. The result has referencevalue for preparing and producing the same kind of products.