TY - JOUR

T1 - Thermal stability of silicon surface passivation by APCVD Al 2O3

AU - Black, Lachlan E.

AU - Allen, Thomas

AU - Cuevas, Andres

AU - McIntosh, Keith R.

AU - Veith, Boris

AU - Schmidt, Jan

PY - 2014

Y1 - 2014

N2 - We investigate the thermal stability of silicon surface passivation provided by aluminium oxide (Al2O3) films deposited using atmospheric pressure chemical vapour deposition (APCVD) and fired in a belt furnace at a peak temperature of ~810 C. Firing stability is investigated for p- and n-type substrates as a function of Al2O3 film thickness both with and without a plasma-enhanced chemical vapour deposition (PECVD) SiNx capping layer, and for boron-diffused surfaces with a ~10 nm Al2O3 film only. Excellent thermal stability of the passivation is demonstrated, with effective carrier lifetimes in n-type silicon wafers remaining stable or even improving after firing, and lifetimes in p-type wafers initially degrading slightly but recovering to above their initial values following ~10 min illumination by a halogen lamp at ~20 mW/cm 2. Film thickness appears to be unimportant to stability, as does the presence of the capping layer. Surface recombination velocities of less than 3 cm/s for 1.35 Ω cm p-type and less than 2 cm/s for 1.2 Ω cm n-type substrates are measured after firing and illumination. The passivation of boron-diffused surfaces is also shown to improve slightly following firing, with a post-firing saturation current density of 42 fA/cm2 on a diffusion with a sheet resistance of 100 Ω/□ and surface dopant concentration of ~1.3×1019 cm-3. Capacitance-voltage (C-V) measurements show that short firing times result in an initial reduction of the interface defect density Dit and a slight increase of the negative insulator fixed charge density Qf, while longer firing results in a substantial increase in both Qf and Dit.

AB - We investigate the thermal stability of silicon surface passivation provided by aluminium oxide (Al2O3) films deposited using atmospheric pressure chemical vapour deposition (APCVD) and fired in a belt furnace at a peak temperature of ~810 C. Firing stability is investigated for p- and n-type substrates as a function of Al2O3 film thickness both with and without a plasma-enhanced chemical vapour deposition (PECVD) SiNx capping layer, and for boron-diffused surfaces with a ~10 nm Al2O3 film only. Excellent thermal stability of the passivation is demonstrated, with effective carrier lifetimes in n-type silicon wafers remaining stable or even improving after firing, and lifetimes in p-type wafers initially degrading slightly but recovering to above their initial values following ~10 min illumination by a halogen lamp at ~20 mW/cm 2. Film thickness appears to be unimportant to stability, as does the presence of the capping layer. Surface recombination velocities of less than 3 cm/s for 1.35 Ω cm p-type and less than 2 cm/s for 1.2 Ω cm n-type substrates are measured after firing and illumination. The passivation of boron-diffused surfaces is also shown to improve slightly following firing, with a post-firing saturation current density of 42 fA/cm2 on a diffusion with a sheet resistance of 100 Ω/□ and surface dopant concentration of ~1.3×1019 cm-3. Capacitance-voltage (C-V) measurements show that short firing times result in an initial reduction of the interface defect density Dit and a slight increase of the negative insulator fixed charge density Qf, while longer firing results in a substantial increase in both Qf and Dit.

KW - AlO

KW - Silicon

KW - Solar cells

KW - Surface passivation

UR - http://www.scopus.com/inward/record.url?scp=84888332586&partnerID=8YFLogxK

U2 - 10.1016/j.solmat.2013.05.048

DO - 10.1016/j.solmat.2013.05.048

M3 - Article

AN - SCOPUS:84888332586

VL - 120

SP - 339

EP - 345

JO - Solar Energy Materials and Solar Cells

JF - Solar Energy Materials and Solar Cells

SN - 0927-0248

IS - PART A

ER -