Er-related Electroluminescence Research Articles

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.

Evolution from random lasing to erbium-related electroluminescence from metal-insulator-semiconductor structured light-emitting device with erbium-doped ZnO film on silicon

A type of metal–insulator–semiconductor (MIS) structured light-emitting device (LED), where a semitransparent gold (Au) film, a polymethyl methacrylate film, and an erbium (Er)-doped ZnO (ZnO:Er) film on a silicon substrate act as the “M”, “I”, and “S” components, respectively, has been prepared. With increasing forward bias with the positive voltage connected to the semitransparent “M” (Au) electrode, such LED first exhibits random lasing (RL) from the ZnO host itself and is then electroluminescent with the characteristic emissions from the Er3+ ions incorporated into the ZnO host. Based on the energy band diagram and the analysis of carrier transportation for the ZnO:Er-based LED applied with different forward bias voltages, the evolution from the RL to the Er-related electroluminescence as mentioned above has been tentatively explained.

Electroluminescence from light-emitting devices based on erbium-doped ZnO/n-Si heterostructures: Enhancement effect of fluorine co-doping.

We report on erbium (Er) related electroluminescence (EL) in the visible and near infrared (NIR) regions from the light-emitting device (LED) based on the Er-doped ZnO (ZnO:Er)/n-Si isotype heterostructure formed by sputtering ZnO:Er film on n-Si/n+-Si epitaxial wafer. Herein, the ZnO:Er film exhibits n-type in electrical conduction. The aforementioned LED is electroluminescent only under sufficiently high forward bias with the negative voltage connecting to n+-Si substrate. Such forward bias enables the electrons from n-Si to enter into the ultra-thin SiOx (x ≤ 2) layer inherently existing between the ZnO:Er film and n-Si via Poole-Frenkel conduction mechanism and, subsequently, to drift into the ZnO:Er film thus becoming hot electrons, which impact-excite the Er3+ ions to emit characteristic visible and NIR light. Furthermore, the Er-related EL from the aforementioned LED can be significantly enhanced through adopting the strategy of co-doping F- ions into the ZnO host, which brings about twofold primary effects. Firstly, due to the atomic size compensation between F- and Er3+ ions, the ZnO crystal grains become larger to accommodate much more optically active Er3+ ions. Secondly, the partial substitution of F- ions for O2- ions around the Er3+ ion reduces the symmetry of pseudo-octahedral crystal field of Er3+ ion, thus increasing the probabilities of intra-4f transitions of Er3+ ions. We believe that this work sheds light on developing efficient silicon-based LEDs using the Er-doped oxide semiconductors.

Near-infrared electroluminescence from metal-oxide-semiconductor devices with erbium-doped gadolinium oxide on silicon

Metal-oxide semiconductor (MOS) devices with Er-doped gate oxides as the light-emitting layers are considered as one of the most promising strategies to achieve silicon-based electroluminescence (EL). In this work, Er-doped Gd2O3 (Gd2O3:Er) films were grown on silicon by atomic layer deposition. The main cubic Gd2O3 phase and hexagonal Gd9.33(SiO4)6O2 phase were obtained in Gd2O3:Er films after thermal annealing treatment. Moreover, 900 °C and 1100 °C were identified as the optimal annealing temperatures for the photoluminescence from Gd2O3 phase and Gd9.33(SiO4)6O2 phase films, respectively. Based on this, the MOS devices were further fabricated with annealed Gd2O3:Er films as the light-emitting layers. Analysis on the current-voltage characteristics of the MOS devices indicates that the electron transportation at the EL-enabling voltages is dominated by Fowler-Nordheim tunneling. More importantly, Er-related EL in the near-infrared region from MOS devices was detected at ∼1530 nm as a function of the Er dopant concentration. The external quantum efficiency reaches 4% for the 900 °C-annealed Gd2O3:0.47%Er MOS device and 8% for the 1100 °C-annealed Gd9.33(SiO4)6O2:2.97% Er MOS device. It is believed that this work has laid the foundation for developing near-infrared silicon-based emitters using Gd2O3:Er films.

Electroluminescence from light-emitting devices with erbium-doped TiO2 films: Enhancement effect of yttrium codoping

We have recently reported erbium (Er)-related visible and near-infrared (∼1540 nm) electroluminescence (EL) from the light-emitting device (LED) with a structure of ITO/TiO2:Er/SiO2/Si in which TiO2:Er refers to the Er-doped TiO2 film [Zhu et al., Appl. Phys. Lett. 107, 131103 (2015)]. In this work, we codope yttrium (Y) into the TiO2:Er film in the aforementioned LED to achieve the significantly enhanced Er-related visible and ∼1540 nm EL. It is suggested that the Y-codoping leads to a less symmetric and distorted crystal field around the Er3+ ions incorporated into the TiO2 host, thus increasing the probabilities of intra-4f transitions of Er3+ ions. Moreover, the Y-codoping facilitates the dispersion of Er3+ ions into the TiO2 host, which is favorable for reducing the concentration quenching effect on the Er-related EL. For the aforementioned two reasons, the EL from the LED based on the TiO2:Er film can be enhanced by means of codoping Y into the TiO2 host.

Light-emitting devices based on erbium-doped TiO2/p+-Si heterostructures: Engineering of electroluminescence via aluminum co-doping

We have recently reported erbium (Er)-related visible and infrared (∼1540 nm) electroluminescence (EL) from the light-emitting device (LED) based on Er-doped TiO2 (TiO2:Er)/p+-Si heterostructure, triggered by the energy transferred from oxygen-vacancy-related self-trapped excitons (STEs) to Er3+ ions in anatase TiO2. Herein, we further co-dope aluminum (Al) into the TiO2:Er film, which is also used to form heterostructure with p+-Si. The LED based on such heterostructure features the Er-related EL with the substantially suppressed visible emissions and the remarkably enhanced ∼1540 nm emission. The Al co-doping is proved not to substantially affect the amounts of oxygen-vacancy-related STEs and Er3+ ions in anatase TiO2. In this context, the above-mentioned engineering of Er-related EL is tentatively ascribed to the modification of crystal field around the Er3+ ions in anatase TiO2 by the Al co-doping.

Low-voltage driven visible and infrared electroluminescence from light-emitting device based on Er-doped TiO2/p+-Si heterostructure

We report on visible and infrared electroluminescence (EL) from the light-emitting device based on Er-doped TiO2/p+-Si heterostructure. Under a forward bias voltage as low as 5.5 V, the device emits ∼1540 nm infrared light and visible light peaking at 522, 553, 564, and 663 nm, respectively, which are originated from Er3+ intra-4f transitions. It is found that the existence of sufficient oxygen vacancies in TiO2 is critical for triggering the Er-related EL. Furthermore, the energy transfer from the oxygen-vacancy-related excitons in TiO2 matrix to Er3+ ions is supposed to be responsible for the above-mentioned EL.

Electroluminescence properties of GaInP/GaAs:Er,O/GaInP double heterostructure light-emitting diodes at low temperature

Low-temperature Er-related electroluminescence (EL) properties have been investigated in Er,O-codoped GaAs (GaAs:Er,O) light-emitting diode (LED) grown by organometallic vapor phase epitaxy. Under forward bias at 77 K, the EL spectra from a cleaved edge of the LED were dominated by the luminescence due to an Er–2O center, indicating that injected carriers contribute effectively to the excitation of the Er–2O center. Excitation cross-sections of Er ions by current injection were obtained by the current density dependence of the EL intensity and its time response. The excitation cross-sections depended on temperature and the active layer thickness of the LED.

Effect of Space Charge Region Width on Er-Related Luminescence in Reverse Biased Si:Er-Based Light Emitting Diodes

In this paper, an effect of space charge region (SCR) width on Er-related electroluminescence (EL) in reverse biased Si:Er-based light-emitting diodes (LEDs) is under investigation. It is concluded that a trivial widening of the SCR in the examined LEDs with triangular and trapezoidal electric field profiles through SCR does not result in a desirable increase in the Er-related EL intensity. The tunnel transit-time diode structure with a complicated electric field profile through SCR is offered to increase the Er-related EL intensity. The difficulties hampering this process in erbium EL from reverse biased LEDs are under discussion

Room-temperature electroluminescence properties of Er,O-codoped GaAs injection-type light-emitting diodes grown by organometallic vapor phase epitaxy

Room-temperature Er-related electroluminescence (EL) properties have been investigated in Er,O-codoped GaAs (GaAs:Er,O) light-emitting diodes grown by organometallic vapor phase epitaxy. Under forward bias, characteristic emission due to a luminescence center consisting of Er coordinated by O and As was clearly observed at room temperature. The injection current density dependence of the EL intensity and its dynamics revealed extremely large excitation cross section of 1–2×10−15 cm2. The excitation cross section for current injection (σc) is by five orders of magnitude larger than that for optical excitation (σo) in Er-doped fiber amplifiers (10−21–10−20 cm2).

Effect of the breakdown nature on Er-related electroluminescence intensity and excitation efficiency in Si:Er light emitting diodes grown with sublimation MBE technique

The influence of the p–n junction breakdown mechanism on the Er 3+ electroluminescence (EL) intensity and excitation efficiency (an intra 4f transition 4 I 13/2→ 4 I 15/2 of Er 3+ ion at the wavelength of 1.54 μm) has been investigated in Si:Er light emitting diodes (LED) grown with sublimation molecular beam epitaxy (SMBE) method. It is shown that the avalanche LEDs are characterized by a greater Er 3+ EL intensity and excitation efficiency compared with the tunnel LEDs. At the same time, an excessive advance into the avalanche breakdown parameter region leads to microplasma breakdown of the p–n junction, which causes a non-uniform distribution of the drive current density over p–n junction area and an appreciable decrease of the Er 3+ EL intensity. Si:Er LEDs operating in mixed breakdown conditions seem to be more preferable for reaching maximal Er 3+ EL intensity at room temperature, as they provide an optimum combination of high Er 3+ EL excitation efficiency with the uniformity of the p–n junction breakdown.

Extremely Large Er Excitation Cross Section in Er,O-Codoped GaAs Light Emitting Diodes Grown by Organometallic Vapor Phase Epitaxy

ABSTRACTRoom-temperature Er-related electroluminescence (EL) properties have been investigated in Er,O-codoped GaAs (GaAs:Er,O) light emitting diodes (LEDs) grown by organometallic vapor phase epitaxy (OMVPE). Under forward bias, characteristic emission due to a luminescence center consisting of Er coordinated by O and As was clearly observed at room temperature, while the Er-related EL was undetectable under reverse bias. At lower current densities, the EL intensity increased linearly with the current density. Subsequently, the intensity exhibited a tendency to saturate at higher current densities. By analyzing the behavior with a fitting according to rate equations, the excitation cross section of Er ions due to current injection was determined to be approximately 10-15 cm2, which is by five orders in magnitude larger than that for optical excitation in Er-doped fiber amplifiers (10-20∼10-21 cm2).

Study of Er-related Defects in a-Si:H(Er) Films Used in Light Emitting Heterostructures

AbstractDefects relating to Er-doping of hydrogenated amorphous silicon films in amorphous/ crystalline (a-Si:H(Er) / n-Si) heterostructures used as light emitters were studied. Electrical parameters of the defects were evaluated by thermally activated current (TAC) and capacitance (TACap) spectroscopy, and high-frequency (1 MHz) capacitance-voltage (C-V) characteristics measured at 77 K. For charging of the traps, visible light illumination at low temperatures and thermal-bias stress at various temperatures were used. The amplitude of TAC was found to increase monotonically with increase of Er concentration in the a-Si:H film. The traps, with activation energies in the range 0.10 - 0.35 eV and 0.5 - 0.6 eV, were charged under both light and thermal-bias stress, and may be associated with the deep levels in the band-gap of a-Si:H. High-temperature current peaks with activation energies of 0.8-0.9 eV emerged only under thermal-bias stress and were strongly dependent on the charging temperature. It is suggested that these high-temperature thermally activated processes are related to polarization of the Er-O bonds in the amorphous matrix of a-Si:H. C-V measurements show that charging of the structure by negative substrate bias leads to net electron trapping in the a-Si:H(Er) film, whereas charging by positive bias result in net hole trapping. The model of Er-related electroluminescence in a-Si:H(Er) / n-Si heterostructures involving electron-hole recombination via deep levels located in the vicinity of [Er-O] inclusions is discussed.

Electroluminescence studies of Er and SiO co-doped Si layers prepared by molecular beam epitaxy

Er/O co-doped Si light emitting diodes (LEDs) have been fabricated using layer structures prepared by molecular beam epitaxy (MBE). The Er/O doping was realized by sublimation of elemental Er and silicon monoxide simultaneously with Si during MBE growth. Intense Er-related electroluminescence (EL) at 1.54 μm was observed at room temperature from p +-SiGe/i-SiGe-Si/Si:Er/n +-Si LEDs by electron impact excitation under reverse bias. It has been found that the EL intensity was increased with increasing growth temperature of the Si:Er/O layer in the range of 430–575°C. The electrical pumping power dependence of EL intensity has been studied. An excitation cross section value of ∼1×10 −16 cm 2 was estimated based on the experimental data and model fitting. The EL decay behavior under various injection and bias conditions has been studied by time-resolved EL measurements. The overall luminescence decay time is found to strongly depend on the injection parameters. Two types of de-excitation mechanisms due to Auger energy transfer to free carriers introduced by either dopant ionization or carrier injection have been discussed. Both Auger processes play an important role in reduction of the EL intensity when there is a high density of carriers with excited Er ions.

Excitation cross-section and lifetime of the excited state of erbium ions in avalanching light-emitting Si : Er : O diodes

Electroluminescence (EL) characteristics of avalanching silicon diodes fabricated by Er and O co-implantation and subsequent annealing have been studied. Saturation of the Er-related EL intensity is achieved under the avalanche regime at current density an order of magnitude lower than that under the tunnel regime. Under avalanche regime at 300 K, the effective cross-section for excitation of Er 3+ ions is equal to 2.3×10 −16 cm 2 and the lifetime of the excited state is equal to 380 μs being ∼four times higher than these values in tunneling diodes.

Anomalous temperature dependence of erbium-related electroluminescence in reverse biased silicon p–n junction

Electroluminescence (EL) and electrophysical characteristics of erbium and oxygen coimplanted and annealed p–n junctions, characterized by higher values of the Er3+-related EL intensity at ∼1.54 μm in the breakdown regime at 300 K as compared with that at 85 K, have been studied in the temperature range from 85 to 300 K. Hole traps in the Er–O codoped n layer were found to be responsible for the anomalous EL behavior. Er-related EL was observed in the same samples in avalanche breakdown at high temperatures and in tunnel breakdown at low temperatures.

Characteristics of the electroluminescence and photoluminescence emission of erbium ions doped in InP and the energy transfer mechanism

The characteristics of impact excitation of the 1.54-μm emission due to intrashell transitions of 4f electrons of erbium atoms (4I13/2 →4 I15/2) doped into InP were investigated in comparison with the photoluminescence (PL) emission of the same peak from the same sample. The thermal quenching of this Er-related electroluminescence (EL) emission was found to be very small in contrast to the large thermal quenching of the PL emission. The EL emission intensity at room temperature was half that at 77 K, and the temperature dependence of the emission energy and the spectral width was very small. Due to almost temperature-independent nature of the impact excitation process, the quenching of the EL emission intensity reflected directly that of the fluorescence efficiency of this intrashell transitions of Er 4f electrons. Using this result, the temperature dependence of the PL energy transfer efficiency was also obtained. It was also found that the fine structure of the 1.54-μm emission was different between EL and PL. It was speculated that Er atoms on different lattice sites, which were in different crystal fields, were excited depending on excitation processes.