Geometry Controlled White Light Emission and Extraction in CdS/Black-Si Conical Heterojunctions

Abstract

The light emission characteristics of Si nanocrystallites on a chemically etched black-Si surface, coupled with its excellent light extraction feature of nanocone geometry is reported for potential use in future Si-based CMOS-compatible light-emitting applications. As a proof of concept, n-CdS/p+-black-Si conical-heterojunction arrays, fabricated by depositing n-CdS film on vertically standing nanoporous Si nanocones, exhibiting intense white light emission, have been studied. Si nanocone arrays of 1 to 3 μm height were fabricated using a metal-assisted chemical etching technique followed by CdS deposition by pulsed laser deposition. A broad EL emission covering the entire visible spectrum and extending up to the NIR wavelength region (450 to 860 nm) has been achieved at room temperature and low forward bias condition. Improved light extraction characteristics in the nanocone textured geometry of black Si over a planar heterojunction have been corroborated by optical simulation analysis. The enhanced light emission characteristics of n-CdS/p+-black-Si conical-heterojunction arrays at a low bias voltage may open up a new opportunity for CMOS-compatible, low-power-consuming, and highly efficient phosphor-free white LEDs in the near future.

Size-tunable electroluminescence characteristics of quantum confined Si nanocrystals embedded in Si-rich oxide matrix

“…[1][2][3][4] Reducing the dimensions of Si structures below the excitonic Bohr radius of Si ($4.8 nm) results in light emission due to the quantum confinement effect (QCE). [5][6][7][8] Different approaches of light emission through the QCE have been reported to date based on Si nanowires, [9][10][11][12] nanocones, 13,14 colloidal nanocrystals, 15,16 and nanocrystals in the oxide matrix. 5,[17][18][19] Among them, Si nanocrystals (Si NCs) embedded into the SiO 2 matrix are most promising due to chemical stability and wavelength selective size-tunable photoluminescence (PL).…”

Latest Development on Pulsed Laser Deposited Thin Films for Advanced Luminescence Applications

“…Recently, LEDs of different luminescence materials have been fabricated using the PLD technique. Sarkar et al [51] reported a white light emission from CdS/p + −black Si (CdS/p + −bSi) LED, manufactured by laser ablation of n-CdS thin film on a nanoporous Si nanocones fabricated subsequently by means of metal-assisted chemical etching technique. A detailed review of this publication is in Section 5.…”

“…The field emission scanning electron microscope (FESEM) cross-section image of the bSi fabricated on a Si substrate reported by Sarkar et al [51] is shown in Figure 9a. The FESEM micrograph revealed that the bSi formed vertical cone-shaped nanostructures of the diameter between 500 and 700 nm, height between 1 and 3 µM and tips of a few nanometers in diameter.…”

“…As shown in Figure 9f, the SAED pattern of the CdS/bSi heterojunction shows the diffraction rings confirming the polycrystalline nature of the CdS thin film. The SAED pattern also revealed the (002), ( 110) and (112) planes of wurtzite CdS [51]. λ = wavelength (nm), RR = repetition rate (Hz), LF = laser fluence (J cm −2 ), PW = pulse width (ns), LE = laser energy (mJ).…”

“…These variations in the particle morphologies resulted in a significant variation of the shapes of the photoluminescence (PL) spectra depicted in the 13th figure. Figure 11a shows the normalized PL spectra of the bSi, a control CdS thin film and the CdS/bSi heterojunction excited at the wavelength of 325 nm [51]. The PL spectrum of the bSi exhibited a broad band with a maxima around 644 nm assigned to the quantum confinement of the charge carriers present in Si nanocrystals formed on the porous surface area of the bSi nanocones [78][79][80][81].…”