Deep Ultraviolet Light Research Articles

CAD Layout Analysis for Defect Inspection in Semiconductor Fabrication

ABSTRACT We have been witnessing the continuous size reduction in consumer electronics devices with longer battery life. The Application Specific Integrated Circuits allow for integration of multiple electronics devices on the same dice. At the same time optimizing the transistor and device area lowers power consumption. It is a big challenge to develop such semiconductor processes and also to develop methodologies to monitor the process during semiconductor fabrication. After every major fabrication process, the wafer undergoes an inspection to detect any abnormality that may cause chip failure down the line. An optical inspection using Ultra Violet or Deep Ultra Violet light is designed to find the physical defects that might be “visible” on the wafer. In order to find electrical connection failure during fabrication, a separate approach of electron beam inspection is designed for monitoring metallization processes. In this study, we have used Computer Aided Design layout analysis to guide the defect inspection for both optical and electron beam wafer inspections. The goal was to increase the chances of finding critical defects as well as to reduce the cycle time for the inspection and defect characterization. The proposed approach has been compared with the existing baseline inspection results on the same wafer.

Deep-ultraviolet-triggered neuromorphic functions in In-Zn-O phototransistors

In recent years, photoelectronic synaptic devices have emerged as a platform for use in next-generation neuromorphic systems and artificial neural networks (ANNs). In this paper, we report an artificial photoelectronic synapse based on an ion-gel gated In-Zn-O phototransistor. The phototransistor is stimulated by a deep ultraviolet light spike, and it can process and store information in the form of an electric current. Key biological synaptic behaviors were investigated, including excitatory post-synaptic current and paired pulse facilitation. Furthermore, channel conduction can be changed by photoelectric synergy in order to simulate potentiation and depression behavior in the human brain. Most importantly, four forms of spike-timing dependent plasticity learning principles were realized by a photoelectric hybrid stimulation. Our studies provide a path towards hybrid photoelectronic ANNs capable of performing solar-blind sensitive tasks.

Improvement of AlGaN-based deep ultraviolet light-emitting diodes by using a graded AlGaN superlattice hole reservoir layer

The AlGaN-based deep ultraviolet light emitting diodes (DUV-LEDs) with a graded superlattice hole reservoir layer (HRL) can significantly enhance hole injection efficiency, compared with the traditional LED. We have systematically studied by APSYS software. The application of new structure can obtain higher output power and carrier concentrations, and further influence the carrier recombination rate. The DUV-LEDs with a graded superlattice HRL can obviously improve internal quantum efficiency (IQE) and alleviate efficiency droop. The improved performance is mainly attributed to the higher electron potential height and lower hole potential height, so it enhances electron confinement and hole injection. Thereby, the proposed structure effectively improve the photoelectric performance.

Degradation behavior of AlGaN-based 233 nm deep-ultraviolet light emitting diodes

The degradation behavior of AlGaN multiple-quantum well (MQW) deep-ultraviolet light emitting diodes emitting near 233 nm stressed at a constant current of 100 mA over 1000 h of operation has been investigated. A strong reduction of the MQW luminescence in the first 250 h and nearly stable MQW emission power over the remaining operation time is found. Moreover, the emission powers of the MQW peak as well as the emission power of parasitic peaks centered at around 266 and 403 nm are changing in a comparable manner, indicating a common degradation process. Furthermore, the leakage current below the turn-on voltage increases with increasing operation time and the change of the emission power as a function of drive current is stronger in the low current regime compared to higher currents. All effects noted up to now show the strongest impact in the first 250 h of operation. In contrast, the emission power of an additional parasitic emission band centered around 500 nm increases continuously over time. Taken altogether these observations can be explained by the following physical degradation mechanisms: the concentration of charged point defects acting as non-radiative recombination centers in the AlGaN active region increases. In addition, the concentration of point defects acting as centers for trap-assisted radiative recombination outside the active region increases.

Improved deep ultraviolet light photosensitivity of nanocomposite ZnO–Ag films deposited with substrate heating

The structural and photosensing properties of nanocomposite ZnO–Ag films deposited with substrate heating at 300 °C and subsequent post-annealing upto 600 °C are reported. Nanocomposite ZnO–Ag thin films deposited at a substrate temperature of 300 °C and post-annealed in air at 425 °C showed a red shift of surface plasmon resonance peak upto 114 nm. This result is explained using electron transfer mechanism from Ag nanocrystals (NCs) to ZnO NCs and it is inferred that AgO phase was not formed at the interface of ZnO and Ag NCs. These films showed lower dark current values, negligible white light photosensitivity (∼1.35–1.04) and higher photosensitivity (∼5.0 × 103 at 1 V) to deep ultraviolet light (DUV) and demonstrated thermal stability upto 425 °C. However, ZnO–Ag films post annealed at 500 °C–600 °C showed increase of intensity of (100) and (101) planes of ZnO, oxidation of Ag nanocrystals (NCs) and an increment in white light sensitivity (∼1.65 to 2.84) at 1.0 V applied bias. These results are explained using band diagram for ZnO/Ag–NC/AgO phases. Further, films deposited with 600 °C substrate temperature showed higher dark current and photocurrent values. Hot electrons photoexcited in ZnO NCs (with Eg: ∼3.24 eV) upon illumination with DUV light (photon energy range: 4.43–5.63 eV), and the energetic electrons transferred from Ag–NCs into ZnO conduction band in the as-deposited and 425 °C annealed films, contributed to the high photosensitivity at low applied bias of 1.0 V.

NH4 Be2 BO3 F2 and γ-Be2 BO3 F: Overcoming the Layering Habit in KBe2 BO3 F2 for the Next-Generation Deep-Ultraviolet Nonlinear Optical Materials.

KBe2 BO3 F2 (KBBF) is still the only practically usable crystal that can generate deep-ultraviolet (DUV) coherent light by direct second harmonic generation (SHG). However, applications are hindered by layering, leading to difficulty in the growth of thick crystals and compromised mechanical integrity. Despite efforts, it is still a great challenge to discover new nonlinear optical (NLO) materials that overcome the layering while keeping the DUV SHG available. Now, two new DUV NLO beryllium borates have been successfully designed and synthesized, NH4 Be2 BO3 F2 (ABBF) and γ-Be2 BO3 F (γ-BBF), which not only overcome the layering but also can be used as next-generation DUV NLO materials with the shortest type I phase-matching second-harmonic wavelength down to 173.9 nm and 146 nm, respectively. Significantly, γ-BBF is superior to KBBF in all metrics and would be the most outstanding DUV NLO crystal.

Computer-Assisted Design of a Superior Be2BO3F Deep-Ultraviolet Nonlinear-Optical Material.

Deep-ultraviolet (DUV) nonlinear-optical (NLO) materials generating coherent DUV light by a direct second-harmonic-generation (SHG) process have long been pursued as industrially useful lasers. For several decades, KBe2BO3F2 (KBBF) has been regarded as the best DUV-NLO material; it is characterized by a short DUV phase-matching edge of 161 nm and a large SHG coefficient of 0.47 pm/V. However, it suffers a strong layering tendency, hindering the growth of large crystals for commercial use. Here, we use a computer-aided swarm structure searching technique to design an alternative DUV-NLO material with a new atmospheric-pressure phase Be2BO3F2 with a P6̅2 c space group (γ-BBF) that outperforms the DUV-NLO properties of KBBF. The predicted DUV phase-matching edge and SHG coefficient of γ-BBF are 152 nm and 0.70 pm/V, respectively. The structure of γ-BBF reduces the layering tendency compared with KBBF because of the absence of K atoms in the γ-BBF crystal. Our work paves the way for superior DUV-NLO materials that can be grown as large crystals for commercial applications.

Ultraviolet-light-driven carrier density modulation of graphene based field effect transistors under oxygen- and argon atmosphere

The fine-tuning of graphene charge carrier concentrations is an essential factor to approach the integration of highly efficient electronic and optoelectronic devices. Here, we demonstrate the deep ultraviolet light driven doping tunability of graphene-based field effect transistor in presence of oxygen and argon atmosphere. The doping effect and its reversibility are confirmed from the Raman spectroscopy. These results are further corroborated by electrical transport measurements. Our findings provide an efficient, stable and defects free doping methodology to tailor the electrical properties of graphene for its potential application in desired technology.

Tapering-induced enhancement of light extraction efficiency of nanowire deep ultraviolet LED by theoretical simulations

A nanowire (NW) structure provides an alternative scheme for deep ultraviolet light emitting diodes (DUV-LEDs) that promises high material quality and better light extraction efficiency (LEE). In this report, we investigate the influence of the tapering angle of closely packed AlGaN NWs, which is found to exist naturally in molecular beam epitaxy (MBE) grown NW structures, on the LEE of NW DUV-LEDs. It is observed that, by having a small tapering angle, the vertical extraction is greatly enhanced for both transverse magnetic (TM) and transverse electric (TE) polarizations. Most notably, the vertical extraction of TM emission increased from 4.8% to 24.3%, which makes the LEE reasonably large to achieve high-performance DUV-LEDs. This is because the breaking of symmetry in the vertical direction changes the propagation of the light significantly to allow more coupling into radiation modes. Finally, we introduce errors to the NW positions to show the advantages of the tapered NW structures can be projected to random closely packed NW arrays. The results obtained in this paper can provide guidelines for designing efficient NW DUV-LEDs.

Different surface plasmon coupling behaviors of a surface Al nanoparticle between TE and TM polarizations in a deep-UV light-emitting diode.

The formulations and numerical algorithms of a three-level model for studying the Purcell effect produced by the scattering of an air/AlGaN interface and the surface plasmon (SP) coupling effect induced by a surface Al nanoparticle in a two-polarization emission system to simulate the transverse-electric- (TE-) and transverse-magnetic- (TM-) polarized emissions in an AlxGa1-xN/AlyGa1-yN (y > x) quantum well (QW) are built. In reasonably selected ranges of Al content for an AlGaN QW to emit deep-ultraviolet (UV) light, the enhancement (suppression) of TE- (TM-) polarized emission is mainly caused by the SP-coupling (interface-scattering) effect. Different from a two two-level model, in the three-level model the TE- and TM-polarized emissions compete for electron in the shared upper state, which is used for simulating the conduction band, such that either interface-scattering or SP-coupling effect becomes weaker. In a quite large range of emission wavelength, in which the intrinsic emission is dominated by TM polarization, with the interface-scattering and SP-coupling effects, the TE-polarized emission becomes dominant for enhancing the light extraction efficiency of a deep-UV light-emitting diode.

Enhancing Hybrid Perovskite Detectability in the Deep Ultraviolet Region with Down-Conversion Dual-Phase (CsPbBr3–Cs4PbBr6) Films

Hybrid perovskite photodetectors (PDs) exhibit outstanding performance in the ultraviolet-visible (UV-vis) spectrum but have poor detectability in the deep ultraviolet (DUV) region (200-350 nm). In this work, a novel inorganic-hybrid architecture that incorporates a dual-phase (CsPbBr3-Cs4PbBr6) inorganic perovskite material as a down-conversion window layer and a hybrid perovskite as a light capture layer was prepared to achieve faster, highly sensitive photodetection in the DUV spectrum. A dual-phase inorganic perovskite film coated on the back surface of the photodetector enables strong light absorption and tunes the incident energy into emission bands that are optimized for the perovskite photodetector. The presence of Cs4PbBr6 enhances the capture and down-conversion of the incident DUV light. Due to the down-conversion and transport of the DUV photons, a self-driven perovskite photodetector with this composite structure exhibits a fast response time of 7.8/33.6 μs and a high responsivity of 49.4 mA W-1 at 254 nm without extra power supply.

Influence of post-deposition annealing on structural, optical and transport properties of nanocomposite ZnO-Ag thin films

Thin films of ZnO and ZnO-Ag were grown by rf sputter deposition and post-annealed in air in the 300–600 °C temperature range. Annealing caused variation in strain in ZnO films and significant improvement of ZnO in ZnO-Ag films. The partial oxidation of Ag into AgxO upon annealing of ZnO-Ag films in air resulted in increase of transmittance, absorption due to AgxO phase, weakening of surface plasmon resonance absorption due to Ag nanocrystals and an increase in fluorescence. Surface studies indicate temperature induced particle transport cause agglomeration of nanocrystals in ZnO-Ag films during post-annealing. Annealed ZnO films showed a decrease in dark current and a sixteenfold increase in photocurrent at 3 V applied bias under white light illumination due to the formation of charged acceptors / oxygen vacancy centres, which was comparable to the white light photosensitivity of as-deposited ZnO-Ag film. For low applied bias voltages, Metal-Semiconductor-Metal photoconductive detectors made with annealed ZnO-Ag films showed potential for application as efficient deep ultraviolet (DUV) photodetectors with negligible sensitivity to white light and high sensitivity to DUV light.

Compact Deep UV System at 222.5 nm Based on Frequency Doubling of GaN Laser Diode Emission

Laser light sources emitting in the deep ultraviolet wavelength range between 210 and 230 nm are of great interest for spectroscopic applications. Here, a compact DUV diode laser system emitting at a wavelength of 222.5 nm is presented. The system is based on frequency doubling of the laser radiation from a micro-integrated GaN external cavity diode laser module (μECDL) emitting at 445 nm. The μECDL has an optical pump power of 1.4 W with an emission bandwidth of 35 pm. Narrowband laser radiation in continouos wave operation with an output power of 160 μW at 222.5 nm is generated in a single-pass frequency doubling stage with a β-BaB 2 O 4 crystal. The results are suitable to address applications such as spectroscopic investigations of biological samples. The presented concept of a compact and efficient deep ultraviolet laser light source enables the realization of portable systems for which a small footprint and a low power consumption is essential.

AlGaN-based deep UV LEDs grown on sputtered and high temperature annealed AlN/sapphire

The performance characteristics of AlGaN-based deep ultraviolet light emitting diodes (UV-LEDs) grown by metalorganic vapor phase epitaxy on sputtered and high temperature annealed AlN/sapphire templates are investigated and compared with LEDs grown on epitaxially laterally overgrown (ELO) AlN/sapphire. The structural and electro-optical properties of the devices on 350 nm sputtered and high temperature annealed AlN/sapphire show similar defect densities and output power levels as LEDs grown on low defect density ELO AlN/sapphire templates. After high temperature annealing of the 350 nm sputtered AlN, the full widths at half maximum of the (0002) and (101¯2) reflections of the high resolution x-ray diffraction rocking curves decrease by one order of magnitude to 65 arc sec and 240 arc sec, respectively. The curvature of the sputtered and HTA AlN/sapphire templates after regrowth with 400 nm MOVPE AlN is with −80 km−1 much lower than the curvature of the ELO AlN/sapphire template of −160 km−1. The on-wafer measured output powers of 268 nm LEDs grown on 350 nm sputtered and high temperature annealed AlN/sapphire templates and ELO AlN/sapphire templates were 0.70 mW and 0.72 mW at 20 mA, respectively (corresponding to an external quantum efficiency of 0.75% and 0.78%). These results show that sputtered and high temperature annealed AlN/sapphire provide a viable approach for the fabrication of efficient UVC-LEDs with reduced complexity and thus reduced costs.

Fabrication of cerium-doped β-Ga2O3 epitaxial thin films and deep ultraviolet photodetectors.

High-quality cerium-doped β-Ga2O3 (Ga2O3:Ce) thin films could be achieved on (0001)α-Al2O3 substrates using a pulsed-laser deposition method. The impact of dopant contents concentration on crystal structure, optical absorption, photoluminescence, and photoelectric properties has been intensively studied. X-ray diffraction analysis results have shown that Ga2O3:Ce films are highly (2¯01) oriented, and the lattice spacing of the (4¯02) planes is sensitive to the Ce doping level. The prepared Ga2O3:Ce films show a sharp absorption edge at about 250nm, meaning a high transparency to deep ultraviolet (DUV) light. The photoluminescence results revealed that the emissions were in the violet-blue-green region, which are associated with the donor-acceptor transitions with the Ce3+ and oxygen vacancies related defects. A simple DUV photodetector device with a metal-semiconductor-metal structure has also been fabricated based on Ga2O3:Ce thin film. A distinct DUV photoresponse was obtained, suggesting a potential application in DUV photodetector devices.

Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD.

In this work, combined analysis of internal strain effects on optical polarization and internal quantum efficiency (IQE) were conducted for the first time. Deep ultraviolet light extraction efficiency of AlGaN multiple quantum wells (MQWs) have been investigated by means of polarization-dependent photoluminescence (PD-PL) and temperature-dependent photoluminescence (TD-PL). With the increase of compressive internal strain applied to the MQWs by an underlying n-AlGaN layer, the degree of polarization (DOP) of the sample was improved from -0.26 to -0.06 leading to significant enhancement of light extraction efficiency (LEE) as the PL intensity increased by 29.2% even though the internal quantum efficiency declined by 7.7%. The results indicated that proper management of the internal compressive strain in AlGaN MQWs can facilitate the transverse electric (TE) mode and suppress the transverse magnetic (TM) mode which could effectively reduce the total internal reflection (TIR) and absorption. This work threw light upon the promising application of compressively strained MQWs to reduce the wave-guide effect and improve the LEE of deep ultraviolet light emitting diodes (DUV LEDs).

Depletion-mode quantum dots in intrinsic silicon

We report the fabrication and electrical characterization of depletion-mode quantum dots in a two-dimensional hole gas (2DHG) in intrinsic silicon. We use fixed charge in a SiO2/Al2O3 dielectric stack to induce a 2DHG at the Si/SiO2 interface. Fabrication of the gate structures is accomplished with a single layer metallization process. Transport spectroscopy reveals regular Coulomb oscillations with charging energies of 10–15 meV and 3–5 meV for the few- and many-hole regimes, respectively. This depletion-mode design avoids complex multilayer architectures requiring precision alignment and allows us to adopt directly best practices already developed for depletion dots in other material systems. We also demonstrate a method to deactivate fixed charge in the SiO2/Al2O3 dielectric stack using deep ultraviolet light, which may become an important procedure to avoid unwanted 2DHG build-up in Si MOS quantum bits.

Analysis on Photo Emission and Absorbing Spectrum on GaN Sample by Finite Difference Time Domain Method

III-Nitride semiconductors are especially capable for both electronics and optical devices. The capability of the III-Nitride semiconductors as light emitters to extent the electromagnetic spectrum from deep ultraviolet light, throughout the whole visible region, and into the infrared part of the spectrum, is a significant characteristic, making this material indispensable for the areas of light emitting devices. The near and far field characteristics of the GaN samples are studied by affecting the finite-difference time domain (FDTD) technique. The far region spreading characteristics at diverse incident angles are also conferred. In addition, the spreading field would be concentrated and the transmission efficiency could be enhanced by the phase shift caused by the dielectric substrate. The intended of optoelectronic devices fictitious from III-Nitride materials is supported by acquaintance of refractive index and absorption coefficient of these materials.

便携式深紫外280 nm半导体物证探测光源的研制及应用

便携式深紫外280 nm半导体物证探测光源的研制及应用

Improved carrier injection of AlGaN-based deep ultraviolet light emitting diodes with graded superlattice electron blocking layers.

A DUV-LED with a graded superlattice electron blocking layer (GSL-EBL) is demonstrated to show improved carrier injection into the multi-quantum well region. The structures of modified EBLs are designed via simulation. The simulation results show the carrier behavior mechanism of DUV-LEDs with a single EBL (S-EBL), graded EBL (G-EBL), and GSL-EBL. The variation in the energy band diagram around the EBL region indicates that the introduction of GSL-EBL is very effective in enhancing carrier injection. Besides, all DUV-LEDs emitting at 280 nm are grown in the high temperature metal organic chemical deposition system. It is confirmed that the optical power of the DUV-LED with the GSL-EBL is significantly higher than that of the DUV-LED with the S-EBL and G-EBL.