Consider the recombination process via bulk traps in a forward biased $pn$ homojunction diode. The maximum recombination rate is $U_{\text{max}}$. If the electron and the hole capture cross-sections are equal, which one of the following is $\text{FALSE}$?
1. With all other parameters unchanged, $U_{\text{max}}$ decreases if the intrinsic carrier density is reduced.
2. $U_{\text{max}}$ occurs at the edges of the depletion region in the device.
3. $U_{\text{max}}$ depends exponentially on the applied bias.
4. With all other parameters unchanged, $U_{\text{max}}$ increases if the thermal velocity of the carriers increases.