Electrical activity and structural evolution correlations in laser and thermally annealed As-implanted Si specimens

Abstract

Laser-annealed and further thermally annealed arsenic implanted silicon specimens have been investigated in a range of doses from 1 X 10 16 to 5 X 10 16 As/cm 2 , with different experimental techniques: electrical measurements, transmission electron microscopy (TEM), double-crystal x-ray diffractometry (DCD), and extended x-ray absorption fine structure analysis (EXAFS). On the as laser-annealed samples, in the whole range of doses examined, a lattice contraction of the doped layer has been evidenced by DCD, whereas, on the same specimens, EXAFS measurements have shown the presence of a local expansion around substitutional As atoms. The relationship between strain and carrier concentration has been found to be approximately linear and can be described by the presence of a size and an electronic effect, as recently proposed in the literature. The former effect represents the atomic size contribution, while the latter is the strain induced by the variation of the conduction-band minima due to the doping. After a subsequent thermal annealing in a low-temperature range (350-550 °C), a strong deactivation of the dopant has been evidenced by electrical measurements. From the experimentai results, a new model of the first step of the As deactivation phenomenon at low temperature is proposed. It is described by the capture of two electrons from a pair of As atoms in the second neighbor position in the Si lattice, leading to the formation of a positively charged arsenic~vacancy cluster (As 2 V) + , and to the emission of a negatively charged Si selfinterstitial I -. This model takes into account the main phenomena that are experimentally observed simultaneously to the As deactivation, i.e., the transition from a contraction to a dilatation of the strain observed by DCD and the formation of interstitial loops, At relatively high temperatures (650--900 °C), the hypothesis of the coexistence of the clusters and of the observed precipitates has to be taken into account in order to explain the nature of the inactive As. However, whether clustering or precipitation is the dominant phenomenon still remains an open question.

Lattice compression of Si crystals and crystallographic position of As impurities measured with x-ray standing wave spectroscopy

“…Figure 10 shows a plot of the compression versus active electron concentration. Data from Parisini et al 31 and from Cargill et al 2 for ͑220͒ and ͑100͒ surfaces is also included in this figure. Our values for compression are larger than Parisini's.…”

Deactivation of metastable single-crystal silicon hyperdoped with sulfur

“…41,42 In contrast, and as expected, no such increase in n s has been observed upon annealing silicon hyperdoped with shallow dopant impurities (B, P, As, Sb). 4,15,16,20,21 The ionization energies of isolated impurities for these shallow dopants are so small that they are essentially all ionized at room temperature, so producing clusters with smaller ionization energies would not result in an increase in n s . Thus, the deep-level defects studied here provide a unique opportunity for insight to the formation of impurity complexes in supersaturated material.…”

“…As such, its enhanced properties-increased conductivity in the case of shallow dopants and sub-band gap optical absorption in the case of deep-level dopants-deactivate upon subsequent thermal treatment. 4,10,[14][15][16][17][18][19][20][21][22][23] There has been much interest in studying the nature of this deactivation. Studies on silicon hyperdoped with shallow dopants have correlated dopant deactivation (i.e., reductions in conductivity) with the formation of inactive dopant clusters or precipitates, depending upon the dopant element.…”

Stress Effects on As Activation in Si

“…A detailed explanation can be found in Ref. In spite of longer As-Si bond as compared to the Si-Si bond length, there have been many experiments observing lattice contractions in heavily As-doped Si, which have been attributed to electrons in the conduction band [6,11,12]. To extract the energy vs. strain curve, we calculated the total free energy of 64 atom (or 63 atom with vacancy) supercells using the DFT code VASP [8] in generalized gradient approximation (GGA) with PW91 potential [9].…”