  From first principles calculations, we investigate the stability and physical
properties of single layer h-BN sheet chemically functionalized by various
groups viz. H, F, OH, CH3, CHO, CN, NH2 etc. We find that full
functionalization of h-BN sheet with these groups lead to decrease in its
electronic band gap, albeit to different magnitudes varying from 0.3 eV to 3.1
eV, depending upon the dopant group. Functionalization by CHO group, in
particular, leads to a sharp decrease in the electronic band gap of the
pristine BN sheet to ~ 0.3 eV, which is congenial for its usage in transistor
based devices. The phonon calculations on these sheets show that frequencies
corresponding to all their vibrational modes are real (positive), thereby
suggesting their inherent stability. The chemisorption energies of these groups
to the B and N atoms of the sheet are found to lie in the range of 1.5 -6 eV.
