Can I catch a single photon with webcam's CMOS or CCD sensors? I thought it would be nice to capturing single photons using a webcam's sensor due to simplicity. 
I've read that ccd and cmos sensors have a certain percent of quantum efficiency. What about webcam's sensors? Is it possible to catch single photons sourced by a laser with a webcam?
 A: First, webcams do use CCD or CMOS sensors, usually whichever chip is cheapest at the time.
You can catch photons, but not reliably.  In other words, for every photon that you catch, you will miss several.  There will also be a noise signal, typically equivalent to many photons,
Consider a CCD sensor.  When a photon arrives, it may successfully excite an electron which is then caught in a well.    On the other hand, if it hits the sensor at a wrong location or it doesn't get absorbed close enough to the well, then its electron is lost, leaving no signal.  At the same time, there will be electrons that, due to random thermal excitation, end up in a well even though there was no photon.  This is called the dark current and it adds noise to the image.  It can be reduced by chilling the sensor.  The sensor also must convert the electrons that have been trapped in the well into an electrical signal.  This process also adds noise.
There are several ways to improve the signal-to-noise ratio but they all cost money.  Thinned back-illuminated CCDs, for example, improve the photon collection efficiency.  An intensified CCD imager, called ICCD, amplifies the light signal before it reaches the CCD sensor.   An electron multiplying CCD or EMCCD has an electrical amplifier that is more responsive to single electrons.
A: Technology has significantly evolved since this question was posted. Skipper CCD technology implements a recursive non-destructive readout amplifier that allows for sub-electron charge readout  noise with single-photon sensitivity and high detection efficiency (above the Silicon band-gap energy). For more details you can check this paper https://arxiv.org/abs/1706.00028
