The achievement of Si-based white light emission is one of the challenging goals in the field of display and lighting technologies.Generally
there are two methods to produce white light from light-emitting diodes(LEDs):combining three LED chips(red
green
and blue) in one discrete package or as a cluster LED chips
and coating blue indium-gallium-nitride(In-GaN) LED chips with phosphors.In addition
fabricating multilayer devices using different materials that emit lights with different colors
based on the principle of tricolor(red
green
and blue) overlay
white light can also be obtained.ZnS films were deposited on porous silicon(PS) substrate by pulsed laser deposition(PLD)
and the room-temperature photoluminescence spectra of ZnS films
PS and ZnS/PS composite system were measured.The results show that
after ZnS films were deposited
a blueshift of the red emission from PS layer occurs.Then the ZnS/PS sample was cut into three pieces
and annealed in vacuum at 400℃ for 10
20 and 30 min respectively.In the PL spectra of the three annealed samples
there appeared a new green emission band located at about 550 nm compared with the PL spectra of ZnS/PS composite system before annealing
which is ascribed to the defect-center emission of ZnS.With the increase of annealing time
the intensity of the red emission from PS layer decreases
and a redshift of the peak occurs
which is attributed to the optical band gap shrinking of a-Si:H as a function of hydrogen loss during annealing.Combining the blue
green emission from ZnS films with the red emission from PS layers
a broad PL band from 450 nm to 700 nm in the visible region is obtained
exhibiting intensively white light emission.This work offers a cheap route for fabricating a white LED
which is significant for display and lighting technology.