Unformatted text preview: ECE 4-4-0 Hcmewcrk I] Fall 2005 1. Due: Wednesday, September 0?, 2005 (a) A GaAs semiccnductcr crystal is dcped with carhcn atcms. If the carbcn atcms displace
arsenic atcms, dces the crystal beccme an n—type cr p—type material? Why? (b) Fcr a ncnstcichicmetric GaAs whcse crystal structure remains tc he ainc—blende but its
ccmpcsiticnal ratic cf Asta is slightly larger than 1, e. g. 1.005. Assume that the erscess As
atcms substitute fcr Ga, and the crystal ccntains nc cther impurities. Is this ncnstcichicmetric
GaAs n—type cr p—type? Why? Amcng the indirect materials listed in Appendix DI, which cne has the smallest band gap
energy, and what is that at rccm temperature? Which cne has the largest band gap energy, and
what is that? Based cn Fig. 3.3, explain why the bandgap energy cf a diamcnd crystal increase (cr decrease)
with respect tc that at rccm temperature when it is cccled tc liquid nitrcgen temperature. (a) It was menlicned in Secticn 3.2 that the crwalent bending model gives false impressicn cf
the lccalizaticn cf carriers. As an illustraticn, calculate the radius cf the electrcn crbit arcund
the dcncr in Fig. 3—12c, assuming a grcund state hydrcgen—like crhit in Si. Ccmpare with the Si lattice ccnstant. Use mn : 0.26 1110 fcr Si.
(b)*Repeat part (a) fer the radius cf an electron crhiting arcund the dcncr in GaAs assuming mll : 0.06? mg fcr GaAs. Ccmpare the radius with the GaAs lattice ccnstant. ...
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