The effects of InP grown by He-plasma assisted epitaxy onquantum-well intermixing

He-plasma assisted InP (He*-InP) layers grown by gas source molecular beam epitaxy (GSMBE) have been employed to enhance quantum well (QW) intermixing induced by rapid thermal annealing in a 1.5 μm InGaAsP QW laser structure. Inserting a 40 nm He*-InP layer just above the active region enhances the blue-shift for anneal temperatures larger than 680°C, and a 42 nm additional blue-shift is obtained at 750°C for samples with the He*InP layer, compared to samples with normal InP replacing the He*-InP. This is accompanied by a reduction in the photoluminescence (PL) intensity for anneal temperatures greater than 600°C and is attributed to the migration of nonradiative defects from the He*-InP layer into the QWs. Insertion of a thin InGaAs layer between the He*-InP layer and the QW blocks the diffusion of these nonradiative defects into the QW. The results indicate that the He*-InP material could prove useful in QW intermixing to achieve integrated optoelectronic devices, in particular for high-frequency devices which require short carrier lifetimes     

FBG-type sensor for simultaneous measurement of force (ordisplacement) and temperature based on bilateral cantilever beam

An improved FBG-type sensor for simultaneous measurement of force (or displacement) and temperature based on the bilateral cantilever beam (BCB) is proposed and demonstrated. The two parts of the beam are subject to opposite forces (or displacements) leading to a red shift for the part of the FBG subject to stretch and to a blue shift for the other one. An FBG bonded to the surface of the middle of the BCB is experimentally demonstrated to have a force sensitivity of ~1.046 nm/N, a sensitivity of the displacement-based strain of ~0.317 nm/mm, and a temperature sensitivity of ~0.190 nm/°C between 0°C and 70°C, respectively     

Thermal tuning of polymer optical fiber Bragg gratings

Bragg gratings in polymethyl methacrylate (PMMA)-based polymer fibers were created and were tuned thermally. It is found that the tuning range is more than 18 nm over a temperature variation of 50°C. More importantly, no hysteresis effect was observed as the gratings were heated up and cooled down     

Low-threshold AlGaN-GaN heterostructure field effect transistorsfor digital applications

The fabrication of an AlGaN-GaN based digital inverter circuit is reported, in which a large gain (up to 180) and a noise margin of ~0.5V have been obtained. The measured temperature coefficient of the switching voltage of the inverter was ~3.5 mV/°C up to 90°C. The simulations predict that such an inverter should operate up to ~230°C     

Exponential curvature-compensated BiCMOS bandgap references

An exponential curvature compensation technique for bandgap references (BGR's) which exploits the temperature characteristics of the current gain β of a bipolar transistor is described. This technique requires no additional circuits for the curvature compensation; only a size adjustment of a bias transistor in a conventional first-order compensated BGR is required. Positive and negative versions of the exponential curvature-compensated BGR have been fabricated using a 1.5 μm BiCMOS process. Average temperature coefficients (TC's) of the negative BGR are measured as 2.4 and 6.7 ppm/°C, and those of the positive BGR are measured as 3.5 and 8.9 ppm/°C over the commercial (0~70°C) and military (-55~125°C) temperature ranges, respectively. These circuits dissipate 0.37 mW with a single 5 V supply, and occupy 270×150 μm² and 290×150 μm² , respectively     

Thermooptic planar polymer Bragg grating OADMs with broad tuningrange

Tunable optical add/drop multiplexers (OADMs) were achieved by combining thermally tunable planar polymer Bragg gratings with optical circulators. The gratings exhibit better than 45-dB reflection with no detectable out-of-band reflection. Apodization was utilized to achieve strong sidelobe suppression, and symmetric gratings with uniform strength across the core and cladding layers were used to minimize coupling to cladding modes. These OADMs have a high-bandwidth utilization (BWU) factor of 0.92, with a minimum channel spacing of 75 GHz. They are tunable at a rate of -0.256 nm/°C. Tuning over a 20-nm range was demonstrated with a single device     

Fictive temperature measurement of single-mode optical-fiber coreand cladding

The fictive temperatures of single-mode optical-fiber core, along with its inner and outer cladding, were measured using an infrared (IR) reflection method on the fiber cross-sectional surface. To allow for usage of a larger IR beam size than the diameter of the fiber core, the cross-sectional area of the fiber was increased by slicing the fiber at an oblique angle, along approximately 3° off the fiber axis direction. The magnitude of the fictive temperature was estimated from the IR peak wavenumber-fictive temperature relation obtained for bulk glasses with the same compositions. The observed fictive temperature was in the range of 1150~1300°C for the core, 1450~1550°C for the inner cladding, and 1620~1660°C for the outer cladding and exhibited good correlation with the fiber cooling rate     

Fabrication of chirped fiber grating with adjustable chirp andfixed central wavelength

We theoretically analyze and experimentally demonstrate a simple method for adjusting the chirp of chirped fiber gratings by temperature, while the central wavelength is temperature insensitive. Chirped fiber grating with tapered cross-section area is mounted under tension in a negative thermal-expansion coefficients material. The central wavelength is determined by the tension, and almost does not vary with temperature after packaging. The chirp can be adjusted by temperature. The grating in the package exhibits a linear variation in chirp of -0.00051 nm/cm/°C, and the temperature coefficient of central wavelength is -0.0018 nm/°C     

Analog ALC crystal oscillators for high-temperature applications

Fundamental mode and third-harmonic mode integrated high-performance automatic level controlled (ALC) crystal oscillators for high-temperature applications (up to 250°C), are described in this paper. These oscillators were designed for a pressure measurement system in high-temperature environments, where the output signal is the difference between both generated frequencies. Frequency variations smaller than 0.0001 ppm/s for each oscillator and a frequency drift of about 2.5 ppm/year of the frequency difference are the measured performance concerning, respectively, the short-term (1 s) and long-term frequency stability of these integrated high performance crystal oscillators over the 30°C-225°C temperature range. Other important characteristics are the very stable and constant oscillation levels (~1.1 Vpp), the small second-harmonic distortion (~60 dR), and the phase noise (~95 dB at 50 kHz shift). The characteristics of these oscillators make them also suitable for many other measurement systems (time, temperature, and other physical and chemical quantities), especially if they are constrained to operate under severe temperature conditions     

Thin-film transistors in polycrystalline silicon by blanket andlocal source/drain hydrogen plasma-seeded crystallization

Thin film n-channel transistors have been fabricated in polycrystalline silicon films crystallized using hydrogen plasma seeding, by using several processing techniques with 600 to 625°C or 1000°C as the maximum process temperature. The TFTs from hydrogen plasma-treated films with a maximum process temperature of 600°C, have a linear field-effect mobility of ~35 cm²/Vs and an ON/OFF current ratio of ~10⁶, and TFTs with a maximum process temperature of 1000°C, have a linear field-effect mobility of ~100 cm²/Vs and an ON/OFF current ratio of ~10⁷. A hydrogen plasma has also then been applied selectively a in the source and drain regions to seed large crystal grains in the channel. Transistors made with this method with maximum temperature of 600°C showed a nearly twofold improvement in mobility (72 versus 37 cm² /Vs) over the unseeded devices at short channel lengths. The dominant factor in determining the field-effect mobility in all cases was the grain size of the polycrystalline silicon, and not the gate oxide growth/deposition conditions. Significant increases in mobility are observed when the grain size is in order of the channel length. However the gate oxide plays an important role in determining the subthreshold slope and the leakage current     

高效高亮度硅基顶发射有机电致发光器件的研制

以半透明超薄金属银作为阴极,紫外臭氧处理的厚金属银作为阳极,制备了高效率高亮度的黄光硅基顶发射有机发光器件。当电压为9V时,器件的最大电流效率为4.9cd/A,当电压为17V时,器件的亮度达到14 040cd/m2。通过增加掺杂浓度及阳极厚度对器件结构进一步优化后,器件性能显著提高,其电流效率在外加电压为10V时达到11cd/A,相应亮度为21 748cd/m2.顶发射器件中存在的微腔效应能有效提高器件的发光效率以及亮度,但是也会使器件的共振波长随着观察视角的增大而蓝移。由于采用合适的发光材料,本实验制备的器件的发光峰值在0°~75°视角范围内几乎没有变化。     

High temperature operation of circular-grating surface-emitting DBRlasers fabricated on an InGaAs/GaAs structure

We demonstrate high temperature operation of circular-grating surface-emitting distributed Bragg reflector lasers. The structure is a strained InGaAs/GaAs double quantum well. Circular gratings are defined by electron beam lithography. No epitaxial regrowth is used. A surface emission power of over 40 mW under pulsed operation at temperatures of up to 80°C is obtained without saturation. A fixed single mode operation was achieved over a temperature range of 60 degrees     

Strong 157 nm F2-laser photosensitivity-locking ofhydrogen-loaded telecommunication fibre for 248 nm fabrication oflong-period gratings

Strong (>20 dB) long-period fibre gratings were fabricated by combining F₂-laser photosensitivity-locking of hydrogen-soaked telecommunication fibre and KrF-laser grating formation. The 157 nm pretreatment permanently enhances the fibre photosensitivity response to the low-energy 248 nm photons. Thermal annealing at 120°C for 24 h improves the grating stability without diminishing the enhancement     

High-temperature sensitivity of long-period gratings in B-Gecodoped fiber

We report an investigation of thermal properties of long-period fiber gratings (LPFGs) of various periods fabricated in the conventional B-Ge codoped fiber. It has been found that the temperature sensitivity of the LPFGs produced in the B-Ge fiber can be significantly enhanced as compared with the standard telecom fiber. A total of 27.5-nm spectral shift was achieved from only 10°C change in temperature for an LPFG with 240-μm period, demonstrating a first ever reported high sensitivity of 2.75 nm/°C. Such an LPFG may lead to high-efficiency and low-cost thermal/electrical tunable loss filters or sensors with extremely high-temperature resolution. The nonlinear thermal response of the supersensitive LPG was also reported and first explained     

Temperature-tuned 90° phase-matching properties of LiB3O5

A single LiB₃O₅ crystal cut normal to x(=a) and z(=b) can be used for the 90° phase-matched SHG at 0.475-0.875 μm by heating the crystal from ~20 to 320°C. The improved Sellmeier's equations and new formula of the temperature variation of the refractive indexes are presented     

Characterization of highly doped n- and p-type 6H-SiCpiezoresistors

Highly doped (~2×10¹⁹ cm^-3) n- and p-type 6H-SiC strain sensing mesa resistors configured in Wheatstone bridge integrated beam transducers were investigated to characterize the piezoresistive and electrical properties. Longitudinal and transverse gauge factors, temperature dependence of resistance, gauge factor (GF), and bridge output voltage were evaluated. For the n-type net doping level of 2×10¹⁹ cm^-3 the bridge gauge factor was found to be 15 at room temperature and 8 at 250°C. For this doping level, a TCR of -0.24%/°C and -0.74%/°C at 100°C was obtained for the n- and p-type, respectively. At 250°C, the TCR was -0.14%/°C and -0.34%/°C, respectively. In both types, for the given doping level, impurity scattering is implied to be the dominant scattering mechanism. The results from this investigation further strengthen the viability of 6H-SiC as a piezoresistive pressure sensor for high-temperature applications     

Optimization of gate oxide N2O anneal for CMOSFET's atroom and cryogenic temperatures

This paper presents a study of the impact of gate-oxide N₂ O anneal on CMOSFET's characteristics, device reliability and inverter speed at 300 K and 85 K. Two oxide thicknesses (60 and 110 Å) and five N₂O anneal conditions (900~950°C, 5~40 min) plus nonnitrided process and channel lengths from 0.2 to 2 μm were studied to establish the correlation between the nitrogen concentration at Si/SiO₂ interface and the relative merits of the resultant devices. We concluded that one simple post-oxidation N₂O anneal step can increase CMOSFET's lifetime by 4~10 times, effectively suppress boron penetration from the P⁺ poly-Si gate of P-MOSFET's without sacrificing CMOS inverter speed. We also found that the benefits in terms of the improved interface hardness and charge trapping characteristic still exist at cryogenic temperature. All these improvements are found to be closely correlated to the nitrogen concentration incorporated at the Si/SiO₂ interface. The optimal N₂O anneal occurs somewhere at around 2% of nitrogen incorporation at Si/SiO₂ interface which can be realized by annealing 60~110 Å oxides at 950°C for 5 min or 900°C for 20 min     

Low threshold room temperature pulsed and -57°C CW operationsof 1.3 μm GaInAsP/InP circular planar buried heterostructuresurface-emitting lasers

Room temperature pulsed lasing operation of a 1.3-μm GaInAsP/InP vertical-cavity surface-emitting laser has been achieved by using an effective carrier confinement of circular planar buried heterostructure (CPBH) and high reflectivity SiO₂/Si dielectric multilayer mirrors. The threshold current for a device having a nearly 12-μm-diameter active region was 34 mA at 24°C under pulsed operation. The optimized window cap structure reduces the series resistance to 6~15 Ω. Continuous wave lasing was also obtained up to -57°C, and the threshold below -61°C was still lower than 22 mA     

2-μm GaInSb-AlGaAsSb distributed-feedback lasers

Room temperature continuous-wave operation of 2-μm single-mode InGaSb-AlGaAsSb distributed-feedback (DFB) lasers has been realized. The laser structure has been grown by solid source molecular beam epitaxy (MBE). Single-mode DFB emission is obtained by first-order Cr-Bragg gratings on both sides of the laser ridge. For a cavity with 900 μm length and 4 μm width, the threshold currents are around 20 mA and the continuous-wave output power is 10 mW at a drive current of 200 mA at 20°C. Monomode emission with sidemode suppression ratios of 31 dB has been obtained