Silicon-based Light-emitting Devices Research Articles

Near-infrared and mid-infrared light emission of boron-doped crystalline silicon.

The bottleneck in achieving fully integrated silicon photonics lies in silicon-based light-emitting devices that are compatible with standard CMOS technology. Dislocation loops created by implanting boron into silicon and annealing represent an enticing strategy to transform highly inefficient silicon into a luminescent material. However, the emission at telecommunication wavelength suffers from the strong thermal quenching effect, resulting in low efficiency at room temperature. Here, we applied a new deep cooling process to address this issue. Interestingly, we find that electrons and holes recombine through defects emitting two photons, one in near infrared (NIR, 1.3∼1.6 µm) and the other in mid-infrared band (MIR, around 3.5 µm). The photoluminescence intensity at NIR increases three fold when the temperature increases from 77 K to 300 K. Furthermore, the NIR light emission of reverse biased silicon diodes was significantly enhanced compared to forward bias, emitting the maximum output power of 42 nW at 60 mA. The results offer new opportunities for the development of infrared light sources in integrated circuits.

Electroluminescence from Silicon-Based Light-Emitting Devices with Erbium-Doped ZnO Films: Strong Enhancement Effect of Titanium Codoping.

We report on the visible and near-infrared electroluminescence (EL) from the light-emitting device (LED) based on the erbium (Er)-doped ZnO (ZnO:Er)/SiO2/n+-Si heterostructure, wherein an ∼10 nm thick SiO2 intermediate layer serves as the energy plateau for producing hot electrons, which come from n+-Si via the trap-assisted tunneling mechanism. These hot electrons excite the doped Er3+ ions by inelastic collision, enabling the Er-related EL from the aforementioned LED. More importantly, by means of codoping the appropriate content of titanium (Ti) into the ZnO:Er film, the aforementioned Er-related emissions can be significantly enhanced. The density functional theory calculations indicate that the Ti-codoping improves rather than degrades the symmetry of the crystal field around the optically active Er3+ ions, hence not increasing the intra-4f transition probabilities of Er3+ ions. However, it is found that Ti-codoping nearly eliminates the segregation of Er3+ ions near the ZnO/SiO2 interface. Moreover, Ti-codoping is derived to result in a number of Zn vacancies, which provide the sites for incorporating Er3+ ions in the ZnO matrix. For the above two reasons, the Ti-codoping promotes the incorporation of optically active Er3+ ions into the ZnO matrix, thus enhancing the EL from the aforementioned LED.

Electroluminescence from silicon-based light-emitting devices with erbium-doped TiO2 films annealed at different temperatures

We have previously developed silicon-based light-emitting devices (LEDs) with luminescent erbium (Er)-doped TiO2 (TiO2:Er) films [Yang et al., Appl. Phys. Lett. 100, 031103 (2012)]. In an LED therein, the TiO2:Er film is sandwiched between the ITO film and heavily boron-doped p-type silicon (p+-Si). In this work, we have investigated the electroluminescence (EL) from two LEDs with the TiO2:Er films annealed at 650 and 850 °C, respectively. It is revealed that between the TiO2:Er film and p+-Si, there is an intermediate silicon oxide (SiOx, x ≤ 2) layer and its thickness increases from ∼4 to 8 nm with the increase of annealing temperature from 650 to 850 °C. Interestingly, the thickness of the intermediate SiOx layer is found to exhibit a profound impact on the EL from the LED with the TiO2:Er film on p+-Si. The EL from the LED with the 650 °C-annealed TiO2:Er film is activated only under the forward bias with the positive voltage connecting to the p+-Si substrate. Such EL consists of the oxygen-vacancy-related emissions from TiO2 host and the characteristic visible and ∼1540 nm emissions from the Er3+ ions, while the EL from the LED with the 850 °C-annealed TiO2:Er film can only be enabled by the reverse bias with the negative voltage applied on the p+-Si substrate. Such EL features only the visible and ∼1540 nm emissions from the Er3+ ions. The difference in the EL behaviors of the two LEDs as mentioned above is found to be ascribed to the different electrical conduction mechanisms.

High Optical Power Density Forward-Biased Silicon LEDs in Standard CMOS Process

This letter presents three low-operating-voltage silicon-based light-emitting devices (Si-LEDs) designed and made in a commercial standard 0.18- $\mu $ m CMOS process without any modification. The Si-LEDs with a new three-terminal and wedge-shaped forward-biased carrier-injection-type p+-n junction structure, have high optical powers. The output power increases by two orders of magnitude up to $1.78~\mu $ W without saturation when the forward current is increased from 20 mA to 200 mA. The light-emitting area is the n-type drift region between the n+ region and p+ region. When the forward current increases to 200 mA, the optical power density exceeds 30 nW $\,\cdot \,\mu $ $\mathrm{m}^{-2}$ the power conversion efficiency and external quantum efficiency are $\sim 2\times 10^{\mathrm {\mathbf {-6}}}$ and $8.3\times 10^{\mathrm {\mathbf {-6}}}$ , respectively, higher than all other forward-biased Si-LEDs previously reported to have used CMOS processes without any modification.

Silicon-Based Light-Emitting Devices Based on Ge Self-Assembled Quantum Dots Embedded in Optical Cavities

Highly efficient light-emitting devices operating in 1.3-1.6 μm wavelength range are realized by combining optical cavities and Ge self-assembled quantum dots (QDs) grown on SOI wafers by molecular beam epitaxy (MBE). Different types of optical cavities, including photonic crystal (PhC) nanocavities, microdisks, and microrings, are fabricated to enhance the light emission efficiency at room temperature. Sharp resonant peaks with Q-factor on the order of 103 are observed in the micro-photoluminescence (μPL) spectrum. Through numerical simulation, these peaks are well identified as the corresponding cavity modes. The emission performances of these devices are also investigated by performing pumping-power- and geometric-parameter-dependent μPL measurements. The resonant wavelength, Q-factor, and emission intensity can be easily manipulated by these parameters.

Temperature-dependent photoluminescence of arsenic-doped Si nanocrystals

The characteristics of temperature-dependent photoluminescence (PL) from Si nanocrystals and effects of arsenic-doping (As-doping) were investigated. The Si nanocrystals on a p-type Si substrate were prepared by low pressure chemical vapor deposition and post-deposition thermal oxidation. The As-doping process was carried out using the gas-phase-doping technique. Temperature-dependent PL from Si nanocrystals exhibited considerable differences between samples with/without As-doping. Phase transition between electron–hole liquid and free exciton was observed in the undoped Si nanocrystals, leading to the increase in PL intensity with temperature less than 50 K. Electron emission from As-doped Si nanocrystals to the p-Si substrate was responsible for the significant increase in PL intensity with temperature greater than 50 K. Characteristics of light emission from Si nanocrystals will facilitate the development of silicon-based nanoscaled light-emitting devices.

High‐Speed Color‐Switching Silicon LEDs

Silicon-based light-emitting devices can be produced by patterning commercial silicon wafers into microscale metal–insulator–semiconductor diodes. In this image, a silicon LED switches from IR (false color – left) to off (middle) to visible (right).

Stable electroluminescence of nanostructured silicon embedded into anodic alumina

An electroluminescent structure based on nanostructured silicon embedded in a layer of anodic alumina has been suggested and fabricated. The heat conductivity of the alumina matrix markedly exceeds that of the silicon-containing insulators. The effective heat removal makes it possible to attain a 0.5% quantum efficiency of electroluminescence, which is comparable with the best parameters of silicon-based light-emitting devices. The physical phenomena responsible for the emission of light by the structure under study are considered.

Electroluminescence from nanostructured silicon embedded in anodic alumina

An electroluminescent structure based on nanostructured porous silicon embedded in a layer of anodic alumina has been suggested and fabricated. The heat conductivity of the alumina matrix markedly exceeds that of the silicon-containing insulators. The effective heat removal makes it possible to attain an 0.5% quantum efficiency of electroluminescence, which is comparable with the best parameters of silicon-based light-emitting devices. The physical phenomena responsible for the emission of light by the structure under study are considered.

Silicon-Based Light-Emitting Devices: Properties and Applications of Crystalline, Amorphous and Er-Doped Nanoclusters

In this paper, we summarize the results of an extensive investigation on the properties of MOS-type light-emitting devices based on silicon nanostructures. The performances of crystalline, amorphous, and Er-doped Si nanostructures are presented and compared. We show that all devices are extremely stable and robust, resulting in an intense room temperature electroluminescence (EL) at around 900 nm or at 1.54 mum. Amorphous nanoclusters are more conductive than the crystalline counterpart. In contrast, nonradiative processes seem to be more efficient for amorphous clusters resulting in a lower quantum efficiency. Erbium doping results in the presence of an intense EL at 1.54 mu m with a concomitant disappearance of the 900-nm emission. This suggests that under electrical pumping Er is excited through an efficient energy transfer from the silicon clusters which hence become dark. We have identified an Auger de-excitation of Er with trapped carriers as the main process competing with radiative emission and limiting EL efficiency. This process is particularly severe in presence of unbalanced carrier injection (electrons versus holes) and can be controlled in properly designed structures. These data are presented and their implications are discussed

Low temperature growth of amorphous Si nanoparticles in oxide matrix for efficient visible photoluminescence

We report a low temperature procedure for the fabrication of highly luminescent silicon nanoparticles in silicon-rich oxide films. A number density over 1012∕cm2 has been achieved for silicon particles of about 3nm in size by plasma-enhanced chemical vapor deposition at a substrate temperature of 30°C. Such deposits, when post-annealed at 500°C for 2 min, manifested a photoluminescence two orders of magnitude more intense than those samples grown at 250°C. Strong photoluminescence in the whole visible light range has been measured in samples prepared with this low-temperature procedure. The present results indicate the feasibility of fabricating silicon-based light-emitting devices with moderate processing temperatures.

Group-IV nanocluster formation by ion-beam synthesis

A short review of our investigations devoted to the use of ion-beam-synthesized nanoclusters for silicon-based light emission and nonvolatile memory effects is presented. Blue-violet light emission is demonstrated based on Ge-implanted silicon dioxide layers thermally grown on silicon substrates. This version of silicon-based light emission relies on Ge-related defects in the amorphous ≡Si–O–Si≡ network. The photoluminescence and electroluminescence are excited by a singlet S0–S1 transition of a neutral oxygen vacancy and by electron injection from the silicon substrate into the silicon dioxide layer, respectively. Whereas the photoluminescence excitation is a well-known mechanism, for the case of electroluminescence an interpretation was performed for the first time in the course of our studies. It was found that the most probable way to excite luminescence centers is the impact excitation by hot electrons. Whereas the injection is explained by trap-assisted tunneling of electrons from the substrate into the oxide, the electrons will be transported via traps or in the SiO2 conduction band. The application of the silicon-based light-emitting devices for an integrated optocoupler arrangement is described. Another application of nanoclusters is based on the investigation of thin Si-implanted silicon dioxide layers for nonvolatile memory devices. First promising results demonstrate that the observed programming window can reach several volts and the devices exhibit excellent retention behavior. A 256 K-nv-SRAM is demonstrated showing a programming window of >1 V for write pulses of 12 V/8 ms.

Progress toward nanoscale silicon light emitters

Impressive advances have been made over the last few years in teaching silicon how to emit light. Recently, light-emitting devices (LEDs) made of porous silicon and other forms of nanoscale silicon have been demonstrated with specifications that start to make them attractive for commercial applications. This paper reviews the state-of-the-art in the materials science and device properties of nanoscale silicon-based LED's, including their integration with microelectronic circuits. Porous silicon and other forms of nanoscale silicon contain crystallites smaller than 10 nm. Their intrinsic optical properties are dominated by quantum confinement, which produces an opening of the bandgap and an increase of the luminescence energy with decreasing nanocrystal sizes. The mechanical, thermal, and electrical properties of porous silicon are strongly degraded compared to those of bulk crystalline silicon. In addition, special techniques should be used to maintain a good passivation of the internal surface and the mechanical integrity of porous silicon. As a result, the design and optimization of LEDs made of nanoscale silicon is difficult. The stability, efficiency, response time, and spectral characteristics of porous silicon LEDs are discussed. The progress toward the integration of porous silicon LEDs with microelectronic circuits is reviewed and a simple alphanumeric display is shown.

Silicon-based visible light-emitting devices integrated into microelectronic circuits

MICROELECTRONIC device integration has progressed to the point where complete 'systems-on-a-chip' have been realized1–3. Now that optoelectronics is becoming increasingly important for information and communication technologies, there is a need to develop optoelectronic devices that can be integrated with standard microelectronics. Conventional semiconductor technology is largely based on crystalline silicon, which (being an indirect bandgap semiconductor) is an inefficient light-emitting material. This has stimulated significant effort towards developing silicon-based optoelectronic components and, of the several strategies explored so far4,5, the use of porous silicon appears the most promising; porous silicon produces high-efficiency, room-temperature, visible photoluminescence6, and its material and optical properties have been studied in detail7,8. But the extreme reactivity and fragility of porous silicon have hitherto prevented its integration with conventional silicon processing technology. We have recently shown9,10 that the thermal and chemical stability of porous silicon can be greatly enhanced — while retaining desirable light-emitting and charge-transport properties — by partial oxidation. Here we take advantage of these improvements in material properties to demonstrate the successful integration of silicon-based visible light-emitting devices into a standard bipolar microelectronic circuit.

Integrating Bipolar Junction Transistors with Silicon-Based Light-Emitting Devices

AbstractSilicon-based optoelectronic devices enable the realization of optoelectronic systems that are compatible with integrated circuit manufacturing technology. This work reports on silicon-based visible light-emitting devices (LEDs) that have been successfully integrated into a standard bipolar fabrication sequence. The basic LED structure consists of a 0.5–1.0μm thick silicon-rich silicon oxide (SRSO) active light-emitting layer formed on a p-type silicon wafer by partial oxidation of porous silicon (PSi), with an n+ doped polysilicon cathode. The LEDs exhibit bright electroluminescence (EL) with a spectral peak between 1.75 and 1.90e. The LEDs are connected in a common-emitter configuration to integrated vertical pnp bipolar driver transistors. This is the first demonstration of an all-silicon visible light emitter / bipolar transistor optoelectronic integrated circuit. The LED device fabrication, process integration, and optoelectronic device characteristics are discussed.

RTCVD growth and applications of epitaxial Si1−xGex alloys

Rapid thermal chemical vapor deposition (RTCVD) is a competing technology for the growth of Si1−xGex strained-layer structures for the development of silicon-based heterojunctions. High-quality epitaxial films with growth temperatures as low as 600°C and 4.5 nm-period superlattices have been demonstrated without the use of ultrahigh-vacuum techniques. Narrow-bandgap-base heterojunction bipolar transistors made of Si/Si1−xGex/Si have been shown to have superior characteristics compared to all-silicon homojunction devices, and extend the scaling limits of bipolar transistors. Finally, RTCVD strained Si1−xGex films exhibit well-resolved band-edge photoluminescence—the first step on the way to developing silicon-based light-emitting devices.