Wavelength tunable photoluminescence (PL) of Si-rich silicon nitride (SRSN) film with buried Si nanocrystals (Si-ncs) grown by plasma enhanced chemical vapor deposition (PECVD) under SiH4 and NH3 environment is investigated. Intense broadband visible emissions tunable from blue to red can be obtained from the as-deposited SiNx thin films with increasing NH3 flow rate from 150 to 250 sccm and detuning the SiH4/NH3 flow ratio during deposition. To date, the normalized PL wavelength of SiNx films after annealing could be detuned over the range of 385~675 nm by decreasing the NH3 flow rate, corresponding to an enlargement on Si-nc size from 1.5~2 to 4~5 nm. The PL linewidth is decreased with increasing ammonia flow rate due to the improved uniformity of Si-ncs under high NH3 flow rate condition. In addition, the PL intensity is monotonically increasing with the blue shift of PL wavelength due to the increasing density of small-size Si-ncs. The ITO/SiNx/p-Si/Al diode reveals highly resistive property with the turn-on voltage and power-voltage slope of only 20 V and 0.18 nW/V, respectively. The turn-on voltage can further reduce from 20 to 3.8 V by improving the carrier injection efficiency with p-type Si nano-rods.