On the local structure of optically active Er centers in Si

Abstract

We report high resolution (<0.05 cm−1) photoluminescence (PL) spectra of erbium implanted float-zone (FZ) and Czochralski grown (CZ) silicon. We show that the PL spectrum of cubic Er centers observed in CZ-Si annealed at 900°C is the dominant emission in FZ-Si for the same annealing conditions. We assign it to isolated, interstitial erbium. We observe also two other kinds of optically active Er centers with lower than cubic site symmetry: (i) O-related (found only in CZ Si) and (ii) those related to radiation defects. We conclude that coimplantation with light elements does not lead to the formation of Er-codopant complexes, but rather to Er forming complexes with implantation induced lattice defects.

Erbium Luminescence in Silicon

“…In high purity float-zone (FZ) silicon the PL intensity of Er is typically 1-2 orders of magnitude lower than in the Czochralski grown (CZ) material. This is obviously related to the at least 2 orders of magnitude higher oxygen content of CZ silicon (about 10 18 cm-3) as compared to FZ and led to speculations that the optically active Εr centers form complexes with oxygen [6], though high resolution PL investigations show that Er-O complex formation is rather limited [9][10][11]. On the other hand it is well known that oxygen can getter Erbium Luminescence in Silcon 85 nonradiative recombimation centers in Si.…”

“…Such a system is expected to combine the ultra sharp, atomic-like emission originating from intra-4f-shell transitions with the efficient pumping via electrons and holes. It is thus not surprising that the optical activity of Er in Si has achieved a lot of attention recently [2][3][4][5][6][7][8][9][10][11][12]. …”

Erbium in Silicon: Possible Light Source for 1.5 μm and Challenge for Defect Physics

“…The occurrence of a highly symmetric, octahedrally coordinated Er-O complex as a dominant emitting center, even in oxygen rich Czochralski (CZ) silicon, seems to be highly unlikely, the more so as it turns out to be also the dominant center in float zone (FZ) Si, which typically contains at least 2 orders of magnitude less oxygen [5]. Though the PL yield of Er in CZ-Si is usually much higher than in FZ Si, a similar relative increase in the PL intensity of the cubic center was observed upon increasing the Er dose (for a constant ion energy) in both materials, indicating that the oxygen content cannot be the limiting factor for the center formation [5]. The most likely candidate responsible for the PL spectrum shown in Fig.…”

“…Because of the narrowness of the implanted layer, however, the total number of Er ions in the sample is rather small (well below 1013 per cm2 for the applied ion energies). Hence the luminescence yield is not very high and high resolution is achieved efficiently only with the use of Fourier spectroscopy [4][5][6]. Different surroundings of the Er ions manifest themselves by different line patterns.…”

“…This wavelength coincides with the transition between the two lowest, spin-orbit split levels of the trivalent erbium ion, which has stimulated extensive investigations of Er doped semiconductors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The wavelength makes Si : Er an interesting candidate for a Si-based, integrable light source for optical communication.…”