Er-doped GaN Research Articles

First-principles investigations of electronic and optical properties of Er-doped GaN involved in ErGaN/ErN quantum well heterostructures

We study the electronic, optic and transport properties of both bulk materials ErN and Er0.125Ga0.875N, where crystallize in zinc-blind and wurtzite structure respectively which are materials involved form a quantum well devices.Based on density functional theory, by applying the full-potential linearized augmented plane-wave method with spin orbit coupling effect. Theanalysis of the electronic properties show that the ErN and Er0.125Ga0.875N has a band gap at 0.79 and 3.38eV respectively. on the other hand, the technology makes possible to stack these materials for a quantum well heterostructure of Er0.125Ga0.875N/ErN.The optical properties such as optical coefficients, refractive index and extinction coefficient are discussed in detail. The transport properties of alloys are investigated using the semi-classical Boltzmann theory as implemented in the BoltzTraP code in conjunction with ab initio electronic structure calculations. Our result shows that Er doping of wide band gap semiconductors is could be a potential candidate for quantum wells devices.

Observation of optical gain in Er-Doped GaN epilayers

Rare-earth based lasing action in GaN semiconductor at the telecommunication wavelength of 1.5 μm has been demonstrated at room temperature. We have reported the stimulated emission under the above bandgap excitation from Er doped GaN epilayers prepared by metal-organic chemical vapor deposition. Using the variable stripe technique, the observation of the stimulated emission has been demonstrated through characteristic features of threshold behavior of emission intensity as functions of pump intensity, excitation length, and spectral linewidth narrowing. Using the variable stripe setup, the optical gain up to 75 cm−1 has been obtained in the GaN:Er epilayers. The near infrared lasing from GaN semiconductor opens up new possibilities for extended functionalities and integration capabilities for optoelectronic devices.

Effect of Erbium doping on GaN electronic and optical properties: First-principles study

In this work, we studied the electronic and optical properties of [Formula: see text] with a concentration [Formula: see text]. Based on a first-principle calculation and using the FP-LAPW full-linearized augmented plane wave method, to see the doping phenomenon with Erbium (Er) [Formula: see text], we used the three approximations: local spin density approximation (LSDA), the LSDA[Formula: see text] with [Formula: see text] is the Hubbard potential and the Becke–Johnson modification (mBJ). Our results show that the values of the structural parameters increase with the substitution of Ga by the Erbium atom. The analysis of the electronic structures in this study shows that the Er-doped GaN has a semi-metallic ferromagnetic character with the LSDA and mBJ approximations and a semiconductor behavior when we apply the Hubbard potential [Formula: see text]. The real and imaginary part of the dielectric function, refractive index, and extinction coefficient are also calculated and presented in the photon energy range up to 14 eV. In the optical spectrum, the intensity of the absorption coefficient is observed in the imaginary part of both doped and undoped GaN in the ultraviolet regions.

Room-Temperature Lasing Action in GaN Quantum Wells in the Infrared 1.5 μm Region

Large-scale optoelectronics integration is strongly limited by the lack of efficient light sources, which could be integrated with the silicon complementary metal-oxide-semiconductor (CMOS) technology. Persistent efforts continue to achieve efficient light emission from silicon in the extending the silicon technology into fully integrated optoelectronic circuits. Here, we report the realization of room-temperature stimulated emission in the technologically crucial 1.5 micron wavelength range from Er-doped GaN multiple-quantum wells on silicon and sapphire. Employing the well-acknowledged variable stripe technique, we have demonstrated an optical gain up to 170 cm-1 in the multiple-quantum well structures. The observation of the stimulated emission is accompanied by the characteristic threshold behavior of emission intensity as a function of pump fluence, spectral linewidth narrowing and excitation length. The demonstration of room-temperature lasing at the minimum loss window of optical fibers and in the eye-safe wavelength region of 1.5 micron are highly sought-after for use in many applications including defense, industrial processing, communication, medicine, spectroscopy and imaging. As the synthesis of Er-doped GaN epitaxial layers on silicon and sapphire has been successfully demonstrated, the results laid the foundation for achieving hybrid GaN-Si lasers providing a new pathway towards full photonic integration for silicon optoelectronics.

Growth, luminescence and magnetic properties of GaN:Er semiconductor thin films grown by molecular beam epitaxy

We report on the growth, surface, luminescence and magnetic properties of 180 nm thick Er-doped GaN thin films grown by molecular beam epitaxy (MBE) on c-sapphire substrates with no buffer layer and with different Er concentrations. In situ reflection high-energy electron diffraction (RHEED) patterns revealed crystalline and uniform growth of the films. The x-ray diffraction (XRD) pattern showed c-axis-oriented growth. Atomic force microscopy (AFM) analysis showed enhancement of surface morphology and smoothness with increasing Er doping, which could be due to minimization of surface defects because of the gettering effect of the rare earth. Scanning area-dependent surface morphology analysis showed a power law dependence indicating the fractal nature of the surface, which is confirmed by the observation of a non-integer D (fractal dimension) value. X-ray photoluminescence spectroscopy (XPS) revealed the formation of a GaN:Er phase and ruled out the presence of Ga and Er metallic and native oxide phases. The semi-quantitative elemental composition of the films was determined using N 1s, Ga 2p3/2 and Er 4d photoemission lines. The Er concentration was estimated from the x-ray photoelectron spectra and found to be between 3.0 and 9.0 at.% (∼1021 atoms cm−3). Photoluminescence (PL) and cathodoluminescence (CL) studies showed visible emission and concentration quenching of Er3+ ions in agreement with reported results. Excitation of the Er3+ ion might be affected by charge trapping due to Er-doping-induced defect complexes. The magnetic measurements carried out by a superconducting quantum interference device (SQUID) showed a ferromagnetic–paramagnetic phase transition at low temperature, contrary to the reported room temperature ferromagnetism in metalorganic chemical vapor deposition (MOCVD)-grown GaN:Er thick films of 550 nm.

Current injection 154 µm light-emitting devices based on Er-doped GaN/AlGaN multiple quantum wells

We report on the growth, fabrication and electroluminescence (EL) characteristics of light-emitting diodes (LEDs) based on Er-doped GaN (GaN:Er) and GaN/AlGaN multiple quantum well (MQW:Er) active layers. The LED structures were grown using metal organic chemical vapor deposition and processed into 300x300 µm2 mesa devices. The LEDs exhibit emission at 1.54 µm, due to Er intra-4f transitions, under forward bias conditions. The 1.54 µm emission properties from LEDs with MQWs:Er and GaN:Er active layers were probed. The LEDs fabricated using MQWs:Er exhibited improved performance as evidenced by a factor of 4 enhancement in the optical power output as compared to conventional GaN:Er based LEDs. The results demonstrate a significant advance in the development of current injected, chip-scale emitters and waveguide amplifiers based on Er doped semiconductors.

Toward the realization of erbium-doped GaN bulk crystals as a gain medium for high energy lasers

Er-doped GaN (Er:GaN) is a promising candidate as a gain medium for solid-state high energy lasers (HELs) at the technologically important and eye-safe 1.54 μm wavelength window, as GaN has superior thermal properties over traditional laser gain materials such as Nd:YAG. However, the attainment of wafer-scale Er:GaN bulk or quasi-bulk crystals is a prerequisite to realize the full potential of Er:GaN as a gain medium for HELs. We report the realization of freestanding Er:GaN wafers of 2-in. in diameter with a thickness on the millimeter scale. These freestanding wafers were obtained via growth by hydride vapor phase epitaxy in conjunction with a laser-lift-off process. An Er doping level of 1.4 × 1020 atoms/cm3 has been confirmed by secondary ion mass spectrometry measurements. The freestanding Er:GaN wafers exhibit strong photoluminescent emission at 1.54 μm with its emission intensity increasing dramatically with wafer thickness under 980 nm resonant excitation. A low thermal quenching of 10% was measured for the 1.54 μm emission intensity between 10 K and 300 K. This work represents a significant step in providing a practical approach for producing Er:GaN materials with sufficient thicknesses and dimensions to enable the design of gain media in various geometries, allowing for the production of HELs with improved lasing efficiency, atmosphere transmission, and eye-safety.

Investigation of low-temperature cathodoluminescence mechanism of Er-doped GaN thick films by ion implantation

Er ions are implanted into the GaN thick films grown by hydride vapor phase epitaxy. The implantation energy is 200 keV and the implantation doses are 1×1013, 1×1014, 1×1015, and 5×1015 atom/cm2, respectively. The effects of the implantation dose and annealing temperature on the GaN band-edge luminescence are investigated. The cathodoluminescence spectra from 82 to 323 K are measured for 1×1015 atom/cm2-implanted GaN annealed at 1100°C. Luminescence peaks at 356, 362, 376, 390, and 414 nm are observed on the 82 K cathodoluminescence spectrum. When the temperature is increased to 150 K, the intensities of the 356 and 414 nm peaks are nearly unchanged and the 362, 376, and 390 nm peaks disappear. The intensity ratio of 538 nm (H11/22→I15/24) and 559 nm (S3/24→I15/24) is increased with the increase in temperature. We try to shed light on the above interesting phenomena.

Hybrid density functional study of optically active Er3+ centers in GaN

Understanding the luminescence of GaN doped with erbium (Er) requires a detailed knowledge of the interaction between the rare-earth dopant and the nitride host, including intrinsic defects and other impurities that may be present in the host material. We address this problem through a first-principles hybrid density functional study of the structure, energetics, and transition levels of the Er impurity and its complexes with N and Ga vacancies, substitutional C and O impurities, and H interstitials in wurtzite GaN. We find that, in the interior of the material, Er$_{\rm Ga}$ is the dominant Er$^{3+}$ center with a formation energy of 1.55 eV; Er$_{\rm Ga}$-$V_{\rm N}$ possesses a deep donor level at 0.61 eV which can assist in the transfer of energy to the 4$f$-electron core. Multiple optically active Er$^{3+}$ centers are possible in Er-doped GaN.

Erbium-doped a-plane GaN epilayers synthesized by metal-organic chemical vapor deposition

A-plane GaN epilayers doped with erbium (GaN:Er) have been grown on r-plane sapphire substrates by metal organic chemical vapor deposition. The 1.54 µm emission properties were probed by photoluminescence (PL) emission spectroscopy and compared with those of c-plane GaN:Er. It was found that the emission intensity from a-plane GaN:Er is 4 times higher than that of c-plane GaN:Er. The intensity of the 1.54 µm emission was found to increase with increasing Er molar flux. A-plane Er-doped GaN epilayers exhibit a small thermal quenching effect, with only a 12% decrease in the integrated intensity of the 1.54 µm PL emission, occurred between 10 and 300 K.

Effects of concentration and thermal annealing on the optical activation of Er implanted into GaN layers

The wide band gap semiconductor, GaN, has emerged as an important host for rare earth-electroluminescence. The annealing behaviour and lattice site location of Er implanted into GaN were studied with the Rutherford Backscattering Spectrometry (RBS)/channelling and photoluminescence (PL) techniques. Also Er site dependence on the annealing temperature and implantation dose has been studied in detail. The optical properties of the Er-doped GaN system, evidencing their dependence on the parameters adopted during the synthesis procedure (Er implantation dose, annealing temperature) have been discussed. RBS/channelling measurements suggested that mostly Er occupy substitutional site and depends on the Er concentration. The main result is the activation of a typical Er giving rise to PL emission in the 1450–1650 nm range, related to radiative 4 I 13/2→4 I 15/2 transitions. Depending on the Er dose, we observe a specific behaviour linked to variation of the annealing temperature that strongly determines PL emission band. We observed a PL spectral shape with the main peak located at 1542 nm and shoulder peak at 1558 nm (and full width at half maximum (FWHM) of 33 nm) with a series of weaker PL structures at 1519, 1572 and 1591 nm, due to the Stark sub-level splitting.

Near infrared photonic devices based on Er-doped GaN and InGaN

Er-doped III-nitride semiconductors have emerged as very attractive materials to achieve photonic devices with multiple functionalities for photonic integrated circuits (PICs). Optical sources and amplifiers based on these materials, particularly GaN and InGaN alloys, can operate at 1.54 μm and are expected to be temperature insensitive and have high signal gain with low noise. There is also the potential for these devices to be electrically pumped and to be integrated onto PICs, which is not possible with either Er-doped silica glasses or narrow bandgap semiconductors like InGaAsP. Here we present results on near infrared emitters and optical amplifiers based on Er-doped GaN/InGaN epilayers grown on different substrates by metal organic chemical vapor deposition (MOCVD). In particular, we report on chip-size current injected emitters and amplifiers fabricated by heterogeneously integrating Er-doped GaN/InGaN epilayers with UV nitride light-emitting diodes. The feasibility of developing electrically pumped optical amplifiers for PIC integration will also be discussed.

Suppression of concentration quenching of Er-related luminescence in Er-doped GaN

Erbium-doped GaN with different doping concentrations were grown by ammonia-source molecular beam epitaxy. The intra-4f-shell transitions related green luminescence were observed by both photoluminescence (PL) and cathodoluminescence (CL) measurements. It was found that concentration quenching of Er-related luminescence was observed in PL measurements while not in CL measurements. The different excitation and relaxation processes are suggested as the cause of the concentration quenching characteristics between PL and CL. The strong Er-related CL intensity in highly doped GaN demonstrates that high energy excitation is a promising approach to suppress the concentration quenching in Er-doped GaN.

Effect of V/III flux ratio on luminescence properties and defect formation of Er-doped GaN

Erbium-doped GaN samples grown with different V/III ratios through gas source molecular beam epitaxy were prepared to investigate the influence of the V/III ratio on the defect formation and the optical activity of the Er-related luminescence center. Obvious V/III ratio dependence was observed in photoluminescence measurement. Positron annihilation spectroscopy measurements suggested that VGa-VN vacancy-complexes formed in these samples and that the VN/VGa ratio depended on the V/III ratio. The generation of Er-VN defect complexes, which act as high optical active luminescence centers, is suggested as the cause of improved optical properties of Er-doped GaN grown with a lower V/III ratio.

Enhancing erbium emission by strain engineering in GaN heteroepitaxial layers

Much research has been devoted to the incorporation of erbium (Er) into semiconductors aimed at achieving photonic integrated circuits with multiple functionalities. GaN appears to be an excellent host material for Er ions due to its structural and thermal stability. Er-doped GaN (GaN:Er) epilayers were grown on different templates, GaN/Al2O3, AlN/Al2O3, GaN/Si (111), and c-GaN bulk. The effects of stress on 1.54 μm emission intensity, caused by lattice mismatch between the GaN:Er epilayer and the substrate, were probed. The emission intensity at 1.54 μm increased with greater tensile stress in the c-direction of the GaN:Er epilayers. These results indicate that the characteristics of photonic devices based on GaN:Er can be optimized through strain engineering.

Optical enhancement of room temperature ferromagnetism in Er-doped GaN epilayers

We report on the enhancement of magnetic properties of Er-doped GaN epilayer structures, grown by metal-organic chemical vapor deposition, with illumination from a light emitting diode. Single and multiple Er-doped epilayers were grown with Er concentrations up to ∼1021 cm−3. All samples exhibited hysteresis behavior at room temperature as measured by an alternating gradient magnetometer. When the samples were illuminated at a wavelength of 371 nm, an increase in saturation magnetization was observed for each sample. The percentage increase for multiple layer samples ranged from 10%–25% indicating possible device applications.

Relationship between defects and optical properties in Er-doped GaN

The density of the vacancy-type defect in Er doped GaN was measured by positron annihilation spectrometry (PAS) and the correlation between the intensity of the Er-related luminescence was studied. A luminescence peak at 558 nm originating from 4 S 3/2 to 4 I 15/2 transition of Er 3+ was observed in Er-doped GaN. The intensity of the luminescence increased with increasing Er concentration and showed the maximum with the Er concentration of around 4.0 at%. The PAS measurements showed that the vacancy-type defect density increased with increasing Er concentration up to 4 at%, and around 4 at% of Er, the formation of defect complex such as V Ga– V N was suggested. The contribution of the defect to the radiative recombination of intra-4 f transition of Er is discussed.

Incorporation sites and luminescence characterizations of Er-doped GaN grown by molecular beam epitaxy

The relationship between optical and structural properties of Er-doped GaN grown by molecular beam epitaxy on sapphire (0 0 0 1) substrates was studied. The Er-related luminescence with wavelength at around 558 nm originated from 4S 3/2 to 4I 15/2 transition was observed. The intensity of the Er-related luminescence increased abruptly with the Er concentration of about 2 at% and showed a maximum at about 4 at%. X-ray diffraction analyses and Rutherford backscattering measurements suggested that most of the Er ions are incorporated into substitutional lattice site with the Er concentration of up to 2 at%, and then begin to occupy interstitial sites. The incorporation site of Er was found to be dependent on the Er concentration. Based on these results, the optically active center of Er in GaN is discussed.

Current-injected 1.54μm light emitting diodes based on erbium-doped GaN

Current-injected 1.54μm emitters have been fabricated by heterogeneously integrating metal organic chemical vapor deposition grown Er-doped GaN epilayers and 365nm nitride light emitting diodes. It was found that the 1.54μm emission intensity increases almost linearly with input forward current. The results represent a step toward demonstrating the feasibility for achieving electrically pumped optical amplifiers for optical communication that possess advantages of both semiconductor optical amplifiers and Er-doped fiber amplifiers.

Vacancy-type defects in Er-doped GaN studied by a monoenergetic positron beam

A relationship between intra-4f transitions of Er and vacancy-type defects in Er-doped GaN was studied by using a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured for Er-doped GaN grown by molecular beam epitaxy. A clear correlation between the defect concentration and the photoluminescence (PL) intensity was observed. The major defect species detected by positrons was identified as a Ga vacancy VGa, and its concentration increased with increasing Er concentration [Er]. For the sample with [Er]=3.3at.%, the maximum integrated intensity of PL was observed. The VGa concentration was above 1018cm−3 and additional vacancies such as divacancies started to be introduced at this Er concentration. For the sample with higher [Er], the PL intensity decreased, and the mean size of vacancies decreased due to an introduction of precipitates and/or metastable phases.