Điện tử học : Diod part 3

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Điện tử học : Diod part 3 Li g h t o u t p u t p Epitaxial layers n+ n+ S u b s t r at eFig. 6.44: A schematic illustration of one possible LED devicestructure. First n+ is epitaxially grown on a substrate. A thin p layeris then epitaxially grown on the first layer.From Principles of Electronic Materials and Devices, Second Edition, S.O. Kasap (© McGraw-Hill, 2002)ht tp: // Mat erials.Usask.Ca Ec EN Eg Ev (b) N doped GaP (a) GaAs1-yPy y < 0.45Fig. 6.45: (a) Photon emission in a direct bandgap semiconductor.(b) GaP is an indirect bandgap semiconductor. When doped withnitrogen there is an electron recombination center at EN. Directrecombination between a captured electron at EN and a holeemits a photon.From Principles of Electronic Materials and Devices, Second Edition, S.O. Kasap (© McGraw-Hill, 2002)htt p:/ /Materials. Usask. Ca Maïch LEDLED daãn coù : VD = 1,6V – 2,2V; ID = 5 – 30mAChoïn trung bình: VD = 2V vaø ID = 10 mAMaïch coù ñieän trôû RD noái vôùi LED vôùi nguoànVcc,caùch tính trò RD tuyø theo trò soá nguoàn Vcc:  R DI D V  V CC D + Vcc V CC  V D RD  R D ID IDVcc = 5V  RD = 200 Ohm Choïn 270 hoaëc 330 Ohm = 9V = 700 Ohm Choïn 680 VD = 12V = 1000 Ohm p p AlGaAs AlGaAs GaAs (a) Ec ~ 0.2 m Ec Electrons in CB No bias 2 eV eVo EF 1.4 eV EF Ec Ev 2 eV (b) Holes in VB Ev With forward bias (c) n+ p p (d) AlGaAs GaAs AlGaAsFig. 6:46: (a) A double heterostructure diode has two junctions whichare between two different bandgap semiconductors (GaAs andAlGaAs). (b) A simplified energy band diagram with exaggeratedfeatures. EF must be uniform. (c) Forward biased simplified energyband diagram. (d) Forward biased LED. Schematic illustration ofphotons escaping reabsorption in the AlGaAs layer and being emittedfrom the device.F r o m P r i n c i p l e s o f E l e c t r o n i c M a t e r i a l s a n d D e v i c e s , S e c o n d E d i t i o n , S . O . K a s a p ( © M c G r a w - H ill, 2 0 0 2 )h t t p : / / M a t e ria ls . U s a s k . C a Current Ge Si GaAs ~0.1 mA Voltage 0 0.2 0.4 0.6 0.8 1.0 Fig.6.4: Schematic sketch of the I-V charact ...