Low Surface Recombination Velocity by Low-Absorption Silicon Nitride on c-Si

We demonstrate that nearly stoichiometric amorphous silicon nitride (SiN
$_{x}$
) can exhibit excellent surface passivation on both
$p$
- and
$n$
-type c-Si, as well as low absorption at short wavelengths. The key process to obtain such a SiN
$_{x}$
is the optimized deposition pressure. The effective carrier lifetimes of these samples exceed the commonly accepted intrinsic upper limit over a wide range of excess carrier densities. We achieve a low
$S_{\rm eff,UL}$
of 1.6 cm/s on 0.85-Ω·cm
$p$
-type and immeasurably low
$S_{\rm eff,UL}$
on 0.47-Ω·cm
$n$
-type silicon passivated by the SiN
$_{x}$
deposited at 290 °C. Capacitance–voltage
$(C-V)$
measurements reveal that this SiN
$_{x}$
has a density of interface states of 3.0 × 10
$^{11}$
eV
$^{-1}$
cm
$^{-2}$
at midgap and an insulator charge of 5.6 × 10
$^{11}$
cm
$^{-2}$
. By comparing the measured injection-dependent
$S_{\rm eff,UL}$
with calculated
$S_{\rm eff,UL}$
by an extended Shockley–Read–Hall (SRH) model, we conclude that either Defect A or B (or both) observed by Schmidt

is likely to dominate the surface recombination at our Si–SiN
$_{x}$
interface. In addition to the outstanding surface passivation, this SiN
$_{x}$
has a low absorption coefficient at short wavelengths. Compared with Si-rich SiN
$_{x}$
of an equivalent passivation, the optimized SiN
$_{x}$
would enhance the photogenerated current density by more than 0.66 mA/cm
$^2$
or 1.40 mA/cm
$^{2}$
for solar cells encapsulated in glass/ethylene-vinyl acetate or operating in air, respectively. The SiN
$_{x}$
described here is ideally suited for high-efficiency solar cells, which require good surface passivation and low absorption from their front surface coatings.