Metastable Defects of Iron-Boron Pair in Silicon
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METASTABLE DEFECTS OF IRON-BORON PAIR INSILICON U. NAKASHIMA AND T. SADOH Department of Electrical Engineering, Kyushu University. Hakozakl, Higashi-ku, Fukuoka 812, Japan
6-10-1
ABSTRACT We have found configurationally metastable Fe-B pairs in SI by using dark or photo capacitance-transient technique combined with minoritycarrier Injection. The metastable pairs are observed as four electrontrapping levels at Ec-0.43 eV, 0.46 eV, 0.52 eV, and 0.54 eV and as two hole-trapping levels at Ev+0.53 eV and 0.48 eV after the injection at 150 K. The production of each level is Investigated under various injection conditions, and the annihilation process is studied by isochronal anneals. Introduction Iron is easily introduced into SI crystals during heat treatments because of Its high solubility and fast diffusivity. In p-type Si, the mobile positively charged interstitial Fe ions (Fe l) are captured by negative substitutional shallow acceptors (A,-), and thus Fei'A,- pairs are formed. The pair formation at around room temperature has been extensively studied 11-41 using deep level transient spectroscopy (DLTS). In 1985, Chantre and Bois [5] have succeeded In the observation of the configurational bistability of Fej between the 1st and 2nd nearest tetrahedral (Td) sites adjacent to Al,. The technique employed is based on the control of Fei charge state during the cooling of the sample to low temperature prior to the DLTS scan. Chantre and Kimerling [61 have also observed the similar bistability for Ga- and In-doped p-Si by using the same technique. However, it is hard to detect the bistability for FeiB, pairs by this method because the donor level (Ev+O.l eV; hereafter labeled HI) corresponding to the 1st nearest site [7] is too shallow. According to the ion pairing theory [2], the pair formation causes pushing of Fei donor level (Fe1j'O) at Ev+0.4 eV (H4) toward the conduction band, and thus the Ist nearest FeiB, pair should have an acceptor level (Fei'/OB,-). The acceptor level has been reported as EC-0.23 eV by Lemke [81 and as 0.29 eV by Brotherton [91, but the level is still not fully clear. On the other hand, Kimerling and Benton [21 have found that FeB, pairs dissociate even below room temperature by minoritycarrier injection for ntp junction. This implies that Fei can sequentially jump from the 1st nearest Td site adjacent to B, to another site by obtaining the electronic energy during recombination process. If very lowlevel injection is carried out at such a low temperature that Fe, can not thermally migrate, It should be possible that Feit Ions remain at configurationally metastable sites bounded to B,-. Hence, it is expected that energy levels for the metastable sites emerge between the acceptor level of stable 1st nearest site FeiB, and the donor level of isolated Fei. We have already found two metastable hole-trapping levels situated at Ev+0.53 eV (H2) and 0.48 eV (H3) by using dark capacitance-transient technique combined with minority-carrier injection [101. In this paper, the properties of metastable Fe B,
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