Reduction of the Linewidths of Deep Luminescence Centers in ${}^{28}\mathrm{Si}$ Reveals Fingerprints of the Isotope Constituents

Dramatic reductions of the linewidths of well-known deep centers in ${}^{28}\mathrm{Si}$ reveal “isotopic fingerprints” of the constituents. The $\sim 1014\mathrm{meV}$ Cu center, thought to be either a Cu pair or an isolated Cu, is shown to contain four Cu atoms, and the $\sim 780\mathrm{meV}$ Ag center is shown to contain four Ag. The $\sim 944\mathrm{meV}$ ${}^{*}\mathrm{Cu}$ center, thought to be a different configuration of a Cu pair, in fact contains three Cu and one Ag, and a new two-Cu two-Ag center is found. The $\sim 735\mathrm{meV}$ center, previously assigned to Fe, actually contains Au and three Cu. This suggests a family of four-atom (Cu, Ag, Au) centers.

Figure 1

The ${\mathrm{Cu}}_0^0$ NP lines ($\sim 1014\mathrm{meV}$) in ${}^{\mathrm{nat}}\mathrm{Si}$ diffused with ${}^{\mathrm{nat}}\mathrm{Cu}$ (top, down-shifted by $62\mu \mathrm{eV}$ for clarity) are compared with those in ${}^{28}\mathrm{Si}$ samples diffused with either ${}^{\mathrm{nat}}\mathrm{Cu}$ (middle) or enriched ${}^{63}\mathrm{Cu}$ or ${}^{65}\mathrm{Cu}$ (bottom). $N=0,\dots ,4$ denotes the number of ${}^{65}\mathrm{Cu}$ in the ${\mathrm{Cu}}_4$ complex. ${\Gamma }_4$ is the ground state transition and ${\Gamma }_3$ is a low lying electronic excited state [2].

Figure 2

NP lines of two centers in ${}^{28}\mathrm{Si}$ containing Cu and either ${}^{\mathrm{nat}}\mathrm{Ag}$, ${}^{107}\mathrm{Ag}$, or ${}^{109}\mathrm{Ag}$. The higher energy center, previously labeled ${}^{*}\mathrm{Cu}$ [9], is here labeled ${\mathrm{Cu}}_3{\mathrm{Ag}}_1$ since it is seen to contain one Ag atom and three Cu atoms. The lower energy ${\mathrm{Cu}}_2{\mathrm{Ag}}_2$ center is seen to contain two Ag and two Cu atoms. Labels $N=0,\dots ,3$ specify the number of ${}^{65}\mathrm{Cu}$ in a given center, while “$a,b,c$” specify the number of ${}^{109}\mathrm{Ag}$, 0, 1, and 2, respectively.

Figure 3

NP lines of the $\sim 780\mathrm{meV}$ Ag center in ${}^{28}\mathrm{Si}$. The electronic states are labeled $F_0$ and $A$ as in previous ${}^{\mathrm{nat}}\mathrm{Si}$ results [15]. Labels “$a$” through “$e$” denote the number of ${}^{109}\mathrm{Ag}$, from 0 to 4, respectively, in the ${\mathrm{Ag}}_4$ complex.

Figure 4

NP lines of the $\sim 735\mathrm{meV}$ ${\mathrm{Cu}}_3{\mathrm{Au}}_1$ complex, previously thought to be related to isolated Fe [20, 21, 22, 23], are compared in ${}^{28}\mathrm{Si}$ diffused with Au and Cu of either almost natural composition (top) or enriched ${}^{65}\mathrm{Cu}$ (bottom). $N=0,\dots ,3$ specifies the number of ${}^{65}\mathrm{Cu}$ atoms in the center. The left-hand and right-hand features come from the ground state and an electronic excited state [21].