Reversible and irreversible effects after oxygen exposure in thick (>1 μm) silicon films deposited by VHF-PECVD on glass substrates investigated by dual beam photoconductivity

Abstract

Metastability and instability effects due to oxygen exposure in thick intrinsic hydrogenated microcrystalline silicon films deposited by very high frequency plasma enhanced chemical vapour deposition on smooth glass substrates were investigated using temperature-dependent dark conductivity, steady state photoconductivity, and sub-bandgap absorption measurements obtained using the dual beam photoconductivity (DBP) method. No significant changes in dark conductivity and photoconductivity were detected even after long-term air exposure of samples in room ambient as well as after oxygen exposure when samples were characterized in oxygen ambient. However, characterization of the oxygen-exposed state in high vacuum caused an increase in dark conductivity and photoconductivity as well as a significant decrease in the sub-bandgap absorption coefficient spectra in the low energy region in samples with I C RS Ͼ 0.40. These changes are partially irreversible for samples I C RS Ͼ 0.80 and mostly reversible for compact materials with significant amorphous fraction. No detectable metastable changes occurred in microcrystalline silicon samples with I C RS Ͻ 0.40 as well as in pure amorphous silicon.Résumé : Nous utilisons la conductivité en obscurité, la photoconductivité stationnaire et des mesures d'absorption sous la bande interdite obtenues de la méthode de photoconductivité à deux faisceaux (DBP), afin d'étudier les effets stables et métastables de l'exposition à l'oxygène de films de silicium microcristallins hydrogénés épais déposés par plasma à haute fréquence augmenté d'un dépôt de vapeur chimique sur un substrat de verre lisse. Nous ne détectons aucun changement de la conductivité en obscurité ni de la photoconductivité, même après une longue exposition à l'air à température ambiante, aussi bien qu'après exposition à l'oxygène où les échantillons sont examinés dans une atmosphère d'oxygène. Cependant, étudier sous vide les échantillons exposés à l'oxygène donne une augmentation de la conductivité en obscurité, aussi bien que de la photoconductivité, en même temps qu'une diminution significative de l'absorption sous la bande interdite dans les échantillons avec I C RS Ͼ 0.40. Ces changements sont partiellement réversibles pour les échantillons avec I C RS Ͼ 0.80 et majoritairement réversibles pour les matériaux compacts avec une fraction amorphe importante. Nous ne détectons aucun changement méta-stable dans les échantillons de silicium microcristallin avec I C RS Ͻ 0.40 ni dans le silicium complètement amorphe. [Traduit par la Rédaction]

Investigation of meta- and in-stability effects in hydrogenated microcrystalline silicon thin films by the steady-state measurement methods

“…Similar investigations were also performed on thick c-Si:H films deposited on the smooth glass as well as those deposited on rough glass substrates with varying crystalline volume fractions. Even though results obtained on those materials were not presented here, the details can be found elsewhere [18]. It was found that reversible and irreversible changes in the measured parameters of amorphous and c-Si:H films with I C RS < 0.30 is very little and no significant change can be recorded as consistent with previous investigations [10,13].…”

Silisyum İnce Filmlerde Taban Malzemelerin Elektronik Kusurlar Üzerine Etkisinin Belirlenmesi

“…Buna karşın yapısında nano ya da mikro kristal yapılar barındıran ve belirli bir ~%10'in üzerinde kristal hacmine sahip silisyum ince filmler atmosferik koşullardan etkilenmekte ve elektronik bozunma yaşamaktadır. [4, 6,13,14,[16][17][18][19][20][21]. Nano ya da mikro kristal silisyumlarda oluşan bu elektronik bozunmalar tamamen geri dönüşümlü olabildiği gibi kısmi ya da tamamen geri dönüşümsüz etkiler de oluşturduğu literatüre rapor edilmiştir [6,13,14,19,20,22,[26][27][28][29].…”

“…[4, 6,13,14,[16][17][18][19][20][21]. Nano ya da mikro kristal silisyumlarda oluşan bu elektronik bozunmalar tamamen geri dönüşümlü olabildiği gibi kısmi ya da tamamen geri dönüşümsüz etkiler de oluşturduğu literatüre rapor edilmiştir [6,13,14,19,20,22,[26][27][28][29].…”