MICROELECTRONICS TECHNOLOGY ECSE 2210
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This 17 page Class Notes was uploaded by Miss Damien Crooks on Monday October 19, 2015. The Class Notes belongs to ECSE 2210 at Rensselaer Polytechnic Institute taught by E. Schubert in Fall. Since its upload, it has received 120 views. For similar materials see /class/224773/ecse-2210-rensselaer-polytechnic-institute in ELECTRICAL AND COMPUTER ENGINEERING at Rensselaer Polytechnic Institute.
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Date Created: 10/19/15
Chapter 9 PNiunction diodes Applications Diode applications Recti ers Switching diodes Zener diodes Varactor diodes Varactor Variable reactance Photodiodes pn junction photodiodes pin and avalanche photodiodes Solar Cells Light Emitting Diodes Lasers Rectifiers Low R in forward direction pnn structure preferred The p and n regions reduce the parasitic resistance Low 10 in reverse Ge is worse than Si Why High voltage breakdown in reverse pnn structure Higher bandgap materials preferred Why Switching diodes Diodes can be used as switching devices Need to change from conducting to nonconducting at high speed Storage time or turnoff transients should be small Add recombination centers to reduce minority carrier lifetimes For example adding 1015cm 3 gold Au to Si reduces hole lifetime to 001 us from 1 us Use narrowbase diodes Amount of charge stored in the neutral region of the diode will be small Zener diodes The breakdown characteristics of diodes can be tailored by controlling the doping concentration Heavily doped p and n regions result in low breakdown voltage Zener effect Used as reference voltage in voltage regulators Region of V operation Varactor diodes Variable reactance diode Voltagecontrolled capacitance of a pn junction can be used in tuning stage of a radio or TV receiver CJ oc VA Where n 12 for an abrupt pn junction However n can be made higher than 12 by suitably changing the doping pro le N A or ND A Linearly graded Hyper abrupt Optoelectronic diodes Many of these diodes involve semiconductors other than Si Use direct bandgap semiconductors Devices to convert optical energy to electrical energy photodetectors generate electrical signal Solar cells generate electrical power Devices to convert electrical energy to optical energy light emitting diodes LEDs laser diodes Optical spectrum correlated with relative eve sensitivitv Photon energy Eph h c 7t Inserting numerical values for h and 0 yields Eph 124 eV um 9t 1 mm lt lnfmxcd lirl ll H I l l l AGWW aidsic 7mg Ga AlAs GaAlt In Si Note Our eye is very sensitive to green light Photodiodes Speci cally designed for detector application and light penetration L q A LN W LP GL assuming uniform photogeneration rate GL 1 dark IL Increasing L light intensity Photodiodes If the depletion width is negligible compared to L11 LP then IL is proportional to light intensity Spectral response an important characteristic of any photo detector Measures how the photocurrent IL varies with the wavelength of incident light Frequency response measures how rapidly the detector can respond to a time varying optical signal The generated minority carriers have to diffuse to the depletion region before an electrical current can be observed externally Since diffusion is a slow process the maXimum frequency response is a few tens of MHz for pn junctions Higher frequency response a few GHZ can be achieved using pin diodes pin photodiodes The iregion is very lightly doped it is effectively intrinsic The diode is designed such that most of the light is absorbed in the i region Under small reverse bias the iregion is depleted and the carriers generated in the iregion are collected rapidly due to the strong electric eld If Wi is the thickness of iregion f l N 1 max carrier transit time across W1 vsat If Wi 5 pm vsat107 cms then fmaX 20 GHZ Pin diodes operating at 13 pm and 155 um are used extensively in optical ber communications pin photodiodes pin photodiodes operating at 155 nm are made on In053GaO47As deposited on InP substrate Contact metal Silicon nitride y InGaAs iInGaAs nInP buffer nInP substrate Back contact metal ghv Bandgap energy versus lattice constant of selected IllV compounds and alloys E5 av 0 54 56 58 60 62 Lattice Constant A Solar cells Solar cells are large area pnjunction diodes designed speci cally to avoid energy losses V00 the open circuit voltage ISC current when device is short circuited n power conversion ef ciency 1m VmP in Spectra inadiance WmZ ym Solar spectral irradiance Wavelenng pm Lightemitting diodes When pn junction is forward biased large number of carriers are injected across the junctions These carriers recombine and emit light if the semiconductor has a direct bandgap For Visible light output the bandgap should be between 18 and 31 eV nyy dome Characteristics of commercial LEDs Semicondncmr Color Peak 101m 1 Ex emgl gidemy Establishsd Material GaAsMPn4 1 Red 1 0650 1 02 1 015 GaAsmrmzN 1 Orangerked 1 0630 1 07 1 1 GaAsWme 1 Yellow 1 0585 1 02 1 1 GaPN 1 Green 1 0565 1 04 1 25 GaPanO Red 1 0700 1 2 1 040 Recent Addm ons AlGaAs 1 Red 1 0050 1 4716 1 2 8 AllnGaP 1 Orange 1 0620 1 6 1 20 AllnGaP 1 Yellow 1 0 585 1 5 1 20 AHnGaP 1 Green 1 0570 1 1 1 6 sac 1 Blue 1 0470 1 002 1 004 GaN 1 Blue 1 0450 1 2 1 05 LED cross section L x graded 04 gt 06 x graded quot39GaAslrlPX L 0 gt 04 quotGaAsll 6PM nGaAs subsLl39ale l a pAlGaAs upper con ning layer AJGaAs active layer nAlGaAs lower con ning layer GaAs subsuale or mick AlGaAs cpilayer c prconlacl pGaPzN nGaP1N nGaP subsuale W W n conmcl segmented to enhance n bottom surface re ec o b W pGeP pAlhlGaP upper cun ning layer AllnCvaP aclive layer nAJ InGaP lower con ning layer nGaAs substrate d