Charge-state-dependent hydrogen-carbon-related deep donor in crystalline silicon

Abstract

The electronic properties of hydrogen in carbon-doped «-type silicon have been studied using deeplevel transient spectroscopy. The results show for the first time that hydrogen in the presence of carbon forms a deep and charge-state-dependent center located ~0.16 eV below the edge of the conduction band. This trap center is a deep donor which is only stable in the positively charged state and anneals after capture of electrons for temperatures T >: 300 K. PACS numbers: 71.55.HtThe properties of semiconductors containing hydrogen (H) have been studied extensively. In this connection, questions regarding the possible charge states of hydrogen have recently received considerable attention. The existence of a hydrogen deep donor level would provide a systematic interpretation of the key experimental results on H in Si, 1,2 and could therefore explain, inter alia, the influence of electric field on H diffusion 3,4 as well as the different diffusion behavior in n-and p-type materials. 5 The problem in detecting such a donor may be that hydrogen drifts during measurements by space-chargelayer methods like deep-level transient spectroscopy (DLTS). The active volume is subject to an electric field in excess of 10 4 V/cm. To examine if H has a donor level in the gap, Ref. 1 proposed hydrogenation experiments in Si samples containing a group-IV impurity (C,Ge). In Ge there indeed exists evidence that H binds to Si and C and forms shallow acceptor levels, 6 but a deep donor level has not been detected so far. Following the suggestion made in Ref. 1, the strategy in this work is to trap H at an isoelectronic carbon (C) impurity in the silicon lattice. Because of the isoelectronic behavior of substitutional carbon in crystalline silicon, a resulting defect level will reflect the principal electronic properties of hydrogen; i.e., it is suited for studying the possible charge states of H in Si.In this work, the results of DLTS measurements carried out on hydrogenated phosphorous-doped c-Si:C are presented. It is shown for the first time that hydrogen in the presence of carbon forms a deep and charge-statedependent center. This trap center is a deep donor with an activation energy located about 0.16 eV below the edge of the conduction band. The existence of this deep center is critically controlled by the position of the Fermi level for temperatures T >: 300 K.Samples are prepared by growing several monocrystalline, phosphorous-doped CZ (Czochralski grown) and FZ (float-zone grown) silicon rods, intentionally doped with different amounts of carbon. Special care was taken to avoid contamination with metallic impurities by using only materials of the highest available purity. The concentration of metallic impurities should therefore be lower than 10 10 cm -3 . The crystals are cut into (100)-oriented wafers which are conventionally cleaned and polished, ir measurements carried out on these wafers show that the added carbon is incorporated on substitutional sites (C 5 ) while oxygen is on interstitial sites (O,-). DLTS measurements ...

Silicon device processing in H-ambients: H-diffusion mechanisms and influence on electronic properties

“…The nature of such interactions depends on the type of impurities. For example, it can deactivate shallow dopants, both acceptor 16,17 and donor 18,19 types, leading to changes in the resistivity of the wafer. Although this effect is an undesirable feature for most cases, it can be used to reversibly alter dopant activity and to form erasable P/N junctions in some future applications.…”

Weakly bound carbon-hydrogen complex in silicon

“…Recently, also carbon-hydrogen complexes in silicon have been addressed. [4][5][6][7][8][9][10][11][12][13] The formation of such complexes may significantly reduce the migration of hydrogen and, thus, be of technological importance. So far only a few carbon-hydrogen complexes have been observed by deeplevel transient spectroscopy ͑DLTS͒, 4-6 photoluminescence, 7,8 and infrared-absorption spectroscopy.…”

What is so strange about hydrogen interactions in germanium?

“…Other shallow levels appear because of hydrogenation, such as the D(H,0) donor. Only the activation of substitutional C has been reported [17] in n-type Si.…”