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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Condition:,a silicon photoconductor at 300K,Background doping,Electron mobility,Hole mobility,Electron lifetime,Hole lifetime,Detector area,Detector length,Bias voltage,Gerneration rate,2.10,Condition:a silicon photocon,1,Calculation:,a)dark current;,b)the excess concentration;,c)the photoconductivity;,d)the device gain.,Solution:,a)The dark current is given by,Calculation:a)dark current;,2,so the dark current is,=,=,so the dark current is=,3,b)The excess carrier density is,c)the photoconductivity is,b)The excess carrier density i,4,d)The gain of the photoconductive detector is,where,So,d)The gain of the photoconduct,5,2.13,Condition:,a GaAs p-i-n detector with,Intrinsic layer width,Optical power density,Photon energy,Absorption coefficient,Device area,Calculation:,the prompt photocurrent of the device.,2.13Optical power density,6,Solution:,The photon flux incident on the detector is,The photocurrent is,Solution:The photon flux inci,7,2.16,Condition:,An avalanche photodetector with,Avalanche region width,The impact ionization coefficient,Calculation:,The multiplication factor,Solution:,The multiplication factor from Eqn.(2.66)is,2.16 Condition:An avalanche p,8,3.8,Condition:,a GaAs p-n,+,junction LED with,Electron diffusion coefficient,Hole diffusion coefficient,n-side doping,p-side doping,Electron minority carrier lifetime,Hole minority carrier lifetime,Calculation:,injection efficiency of the LED,assuming no recombination due to traps.,3.8 Condition:a GaAs p-n+jun,9,Solution:,The electron minority carrier density in p-side is,And hole minority carrier density in n-side is given by,The diffusion length are,Solution:And hole minority car,10,The injection efficiency is(assuming no recombination due to trap),The injection efficiency is(a,11,3.9 The diode in problem 3.8 is used to generate,an optical power of 1 ,the diode area is 1,and the external efficiency is 20。,Calculation:,the forward bias voltage required.,Solution:,The photons generated per second are,3.9 The diode in problem 3.8 i,12,Which are also expressed by,So the current required to generate the photons is,Which are also expressed bySo,13,the current when the diode is forward bias is given by,Solving the above equation for V yields,the current when the diode is,14,3.12,Condition:,a GaAs LED coupled to an optical fiber with,Refractive index for the core layer,Refractive index for the cladding layer,Calculation:,the maximum angle of acceptance for the fiber,and the coupling efficiency for the diode,Solution:,The maximum angle of acceptance is calculated by,The coupling efficiency is,Example 3.7,=32.6,o,=0.29,3.12 Condition:a GaAs LED cou,15,3.15,Condition:,An AlGaAs/GaAs heterojunction LED at 300K with,Injection density for electrons,Injection density for holes,Bandgap of GaAs,Calculation:,the position of emission peak;,the shift in the peak position,if the injection density increased to,3.15 Condition:An AlGaAs/GaAs,16,Solution:From the relationship,for injection density of,the peak position is,half of linewidth,at the bandedge,Solution:From the relationshi,17,for injection density of,Shift of the peak position,for injection density of Shift,18,3.18,Condition:,a heterojunction LED based on GaAs at 300K with,Bias current density,The width of the active layer,Calculation:,the 3db cutoff frequency of the diode.,Solution:,the 3db cutoff frequency is,is related to bias current density by,Thus,3.18 The width of the,19,From Fig.3.6(p140),So the 3db cutoff frequency is calculated as,From Fig.3.6(p140)So the 3db c,20,3.21,Condition:,A GaAs LED with,Output power,The maximum device area,The efficiency of the device,The maximum injection density,Calculation:,the thickness of the active region needed.,Solution:,the optical power delivered by the device is,3.21 The maximum devi,21,where,(=bandgap of GaAs)and,(when ),Solving the above equation for d yields,where(=bandgap of GaAs)and(,22,4.1,Condition:,a GaAs laser with,Cavity length,Bandgap,Calculation:,the number of allowed longitudinal modes,in an energy width,.,Solution:,the frequency of the resonant longitudinal modes is,Where q is an integer.,4.1 Bandgap,C,23,Thus the energy of these modes is,The number of allowed longitudinal modes in an energy width,is,Thus the energy of these modes,24,4.3,Condition:,a Fabry-Perot cavity with,Length,Mirror reflectivity,Absorption loss coefficient,Refractive index,Calculation:,the photon lifetime,Solution:,the cavity loss,is,4.3 Mirror reflectivity,25,The photon lifetime in the cavity is given by,So,The photon lifetime in the cav,26,4.8,Condition:,two GaAs/AlGaAs double heterostructure lasers are fabricated,with Active region thickness,Optical confinement factors,Carrier injection density need to cause lasing,Radiative recombination time,Calculation:,the threshold current densities for the two lasers.,Solution:,the threshold carrier injection densities for the two lasers are,(for both),4.8 Optical confinement,27,So the threshold
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