甩d Vacancies in a semiconductor may be charged positive charge Rydberg states neutral due to negative charge C888生8巴88888888888881 negative charge X in a metal:charge of a vacancy is effectively screened by free electrons they are not available in semiconductors thus,long-range Coulomb potential added positrons may be attracted or repelled trapping coefficient u is function of charge state
Vacancies may be charged V(n) Negative 13.6a0 vacancy For a negative vacancy: 4.8a0 0.1eV Coulomb potential is rather extended but weak 3.5eV V)=-1 r it supports trapping only at V Neutral low temperatures 库仑 vacancy 空位库仑势 at higher temperatures: 势阱 detrapping dominates and vacancy behaves like a vacancy Positive in a metal or a neutral vacancy V(r) vacancy V,(r)= 、1 Positive vacancies repel positrons r
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Positron Trapping in a Single Defect Type Positron source dn,@=-(元，+Kam,0 Thermalization dt Defect-free bulk dna0=-元ana)+Kan,() dt ò Trapping Defect○ solution:decay spectrum Annihilation Annihilation radiation a0n abbreviations: 1 1 The t;and I are measured=k is obtained: t1+Ka 11=1-2, 1,=-a+Kd 网品
Positron Trapping in a Dislocation Positron source the dislocation line (shallow trap)acts as a "funnel"for the trapping in Defect-free bulk deep traps Kstδ Dislocation line b...bulk st ↓9 Vacancy Kt V...vacancy Dislocation-bound vacancy t...deep trap st ..shallow trap Annihilation radiation 入.annihilation rates K,...trapping rates ...detrapping(escape)rate