recombination - 2023 ACF Nationals

Question

This process causes excess carrier concentration to decay to zero at a rate given by the excess carrier concentration over carrier lifetime. For 10 points each:

[10m] Name this process in which an electron from the conduction band falls down to the valence band.

ANSWER: recombination [prompt on electron–hole annihilation or word forms of annihilate; reject “electron–positron annihilation”]

[10e] When current flows in the correct direction in these common semiconductor devices, electrons and holes undergo direct recombination and release a photon.

ANSWER: LEDs [or light-emitting diodes; prompt on diodes]

[10h] Theoretical analysis by William Shockley, William Read, and Robert Hall explained how recombination accompanied by phonons is mediated by these defects. Trace metals like gold form these defects that are distinct from donors or acceptors since their energy level lies in the middle of the band gap.

ANSWER: deep traps [or deep-level traps; accept charge carrier traps; prompt on recombination centers; reject “shallow traps”]

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Summary


2023 ACF Nationals	04/22/2023	Y	21	8.57	71%	14%	0%

Data


Claremont A	Georgia Tech B	0	0	0
UC Berkeley A	Johns Hopkins A	0	10	10
Duke A	Florida B	0	0	0
Yale A	McGill A	0	0	0
MIT A	Michigan A	0	10	10
Minnesota A	Harvard A	0	10	10
NYU A	Minnesota B	0	10	10
Penn A	Houston A	10	10	20
South Carolina A	Purdue A	0	0	0
Virginia A	Imperial A	0	0	0
Illinois A	Chicago C	0	10	10
Ohio State A	Columbia A	0	10	10
North Carolina A	Chicago B	10	10	20
Stanford A	Northwestern A	0	10	10
WUSTL A	Columbia B	10	10	20
UC Berkeley B	WUSTL B	0	10	10
Florida A	Yale B	0	10	10
Penn State A	Georgia Tech A	0	10	10
Rutgers A	Maryland A	0	10	10
Texas A	Rutgers B	0	10	10
Brown A	Cornell B	0	0	0