Abstract
It has been recently suggested that oxygen-related bistable thermal double donors (BTDDs) are responsible for the reduction of minority carrier lifetime and conversion efficiency of novel amorphous-crystalline Si heterojunction solar cells with their base formed from n-type Czochralski-grown (Cz) silicon [M. Tomassini et al., J. Appl. Phys. 119, 084508 (2016)]. To test this hypothesis, we have studied processes associated with carrier emission and capture by BTDDs in p+-n and Schottky barrier diodes on n-type Cz-Si materials with the use of junction capacitance techniques. By means of deep level transient spectroscopy, we have detected electron emission signals from the deep donor state of the BTDD-0 and BTDD-1 centers. The values of activation energy for electron emission (Eem) have been determined as 1.01 ± 0.01 and 0.91 ± 0.01 eV for the BTDD-0 and BTDD-1 centers, respectively. Such high Eem values are very unusual for defects in Si. We have carried out measurements of electron capture kinetics and associated shallow donor–deep donor transformations for the BTDD-0 and BTDD-1 defects at different temperatures in the diodes with different doping levels. Energy barriers for the capture-transformation processes have been determined. It is argued that BTDDs are responsible for carrier trapping in n-type Cz-Si crystals but are not effective recombination centers.
Highlights
It has been known since the 1950s that heat-treatments of oxygen-rich Si crystals in the temperature range 350–500 °C result in the formation of a family of defects with shallow donor levels.[1,2] It has been further found that the defects are helium-like centers with the donor levels E(0/+) and E(+/+2)located in the energy ranges from 0.05 to 0.07 eV below the conduction band edge Ec-(0.05–0.07) eV and Ec-(0.12–0.16) eV, respectively.[3–6] Strong evidence has been presented that the formation of the centers is associated with clustering of interstitial oxygen atoms upon heat-treatments.[7–9] the defects are usually referred to as oxygen-related thermal double donors (TDDs).[8]
It has been recently suggested that oxygen-related bistable thermal double donors (BTDDs) are responsible for the reduction of minority carrier lifetime and conversion efficiency of novel amorphous-crystalline Si heterojunction solar cells with their base formed from n-type Czochralski-grown (Cz) silicon [M
We have studied processes associated with carrier emission and capture by BTDDs in p+-n and Schottky barrier diodes on n-type Cz-Si materials with the use of junction capacitance techniques
Summary
It has been known since the 1950s that heat-treatments of oxygen-rich Si crystals in the temperature range 350–500 °C result in the formation of a family of defects with shallow donor levels.[1,2] It has been further found that the defects are helium-like centers with the donor levels E(0/+) and E(+/+2). The origin of the bistability and possible atomic configurations of the small oxygen clusters, which are associated with BTDDs, have been discussed in ab initio modeling studies.[12–14] It should be noted, that practically all experimental information about the electronic properties of BTTDs has been obtained from observations of the defects in the shallow donor configuration. 24 and 25) has resulted in renewed interest in oxygen-related TDDs.[26–30] These defects have been suggested to be responsible for the reduction of the lifetime of minority carriers and conversion efficiency of Cz-Si based solar cells.[26–30]. It has been speculated in a recent study (Ref. 29) that BTTDs in the deep donor state are the effective recombination centers. A deeper understanding of electronic and recombination properties of BTDDs is required
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