Insulator passivation of In0.2Ga0.8As-GaAssurface quantum wells

The electronic passivation of (100) In_0.2Ga_0.8 As-GaAs surface quantum wells (QWs) using in situ deposition of an amorphous, insulating Ga₂O₃ film has been investigated and compared to standard Al_0.45Ga_0.55As passivation. Nonradiative lifetimes τ_r=1.1±0.2 and 1.2±0.2 ns have been inferred from the dependence of the internal quantum efficiency η on optical excitation density P₀' for the Ga₂O₃ and Al_0.45Ga_0.55As passivated In_0.02 Ga_0.8As-GaAs surface QW, respectively. Beyond identical internal quantum efficiency, the amorphous Ga₂O₃ insulator passivation simplifies device processing, eludes problems arising from lattice-mismatched interfaces, and virtually eliminates band bending in electronic and optoelectronic devices based on a low dimensional system such as quantum wells, wires, and dots     

Chemically etched-mirror GaInAsP/InP lasers--Review

Detailed results on stripe GaxIn1-xAsyP1-y/InP lasers (lambda = 1.3 mum) with chemically etched-mirrors are reviewed. These devices are fabricated from GaInAsP/InP wafers grown by liquid phase epitaxy. A simple stripe laser structure with one etched mirror and one cleaved mirror is proposed. Monolithic passivation has been achieved using a Si3N4film and metal coatings on the etched facets. These processes not only increase the reflectivity of the etched mirrors, resulting in threshold currents even lower than uncoated cleaved devices, but also ease the problem of bonding of the chips on heat sinks. CW operation at room temperature has been achieved. Threshold currents of devices with 10 μm stripe electrodes were about 180-200 mA. Short cavity lasers and integrated monitoring detectors have also been demonstrated.     

Plasma-charging effects on submicron MOS devices

Plasma-charging damage on gate dielectrics of MOS devices is an important issue because of shrinking dimension, plasma nonuniformity, and effects on high-k gate dielectrics. A comprehensive study of plasma-charging effects on the electrical properties of MOS devices was investigated in this work. Shunt diodes were used to estimate the charging polarity distribution. For high-frequency application, the 1/f noise was found to be a promising index for assessing plasma-charging damage. Gate oxynitride formed by two-step nitridation was demonstrated to have better electrical reliability as compared to the conventional one-step nitridation, especially accompanied by amorphous silicon gate electrode. This improvement could be attributed to the relaxation of interface stress by amorphous silicon gate electrode and the suppression of hydrogen effects by gate oxynitride using two-step nitridation. Plasma-charging damage on Si₃N₄ and Ta₂O₅ gate dielectrics with high dielectric constant was also investigated. For MOS devices with Si₃N₄ film, the leakier characteristic and shorter time to breakdown reveal its inferior reliability. For MOS devices with Ta₂O₅ gate dielectric, the trap-assisted current mechanism makes a thicker physical thickness of Ta₂O₅ film more susceptible to plasma-charging-induced damage. Smaller physical thickness of Ta₂O₅ film in MOS devices is favorable due to the better reliability and comparable plasma-induced electrical degradation     

AlGaN/GaN MOS-HEMT With $hbox{HfO}_{2}$ Dielectric and $hbox{Al}_{2}hbox{O}_{3}$ Interfacial Passivation Layer Grown by Atomic Layer Deposition

We have developed a novel AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor using a stack gate HfO₂/Al₂O₃ structure grown by atomic layer deposition. The stack gate consists of a thin HfO₂ (30-A) gate dielectric and a thin Al₂O₃ (20- A) interfacial passivation layer (IPL). For the 50-A stack gate, no measurable C-V hysteresis and a smaller threshold voltage shift were observed, indicating that a high-quality interface can be achieved using a Al₂O₃ IPL on an AlGaN substrate. Good surface passivation effects of the Al₂O₃ IPL have also been confirmed by pulsed gate measurements. Devices with 1- mum gate lengths exhibit a cutoff frequency (fT) of 12 GHz and a maximum frequency of oscillation (f _MAX) of 34 GHz, as well as a maximum drain current of 800 mA/mm and a peak transconductance of 150 mS/mm, whereas the gate leakage current is at least six orders of magnitude lower than that of the reference high-electron mobility transistors at a positive gate bias.     

Effects of Sc2O3 and MgO passivation layerson the output power of AlGaN/GaN HEMTs

The low temperature (100°C) deposition of Sc₂O₃ or MgO layers is found to significantly increase the output power of AlGaN/GaN HEMTs. At 4 GHz, there was a better than 3 dB increase in output power of 0.5×100 μm² HEMTs for both types of oxide passivation layers. Both Sc₂ O₃ and MgO produced larger output power increases at 4 GHz than conventional plasma-enhanced chemical vapor deposited (PECVD) SiN_x passivation which typically showed ⩽2 dB increase on the same types of devices. The HEMT gain also in general remained linear over a wider input power range with the Sc₂O₃ or MgO passivation. These films appear promising for reducing the effects of surface states on the DC and RF performance of AlGaN/GaN HEMTs     

Vertical-cavity surface-emitting laser diodes fabricated by in situdry etching and molecular beam epitaxial regrowth

The authors report the first buried active region vertical-cavity surface-emitting laser diodes fabricated using in situ dry etching and molecular beam epitaxial regrowth. The laser emissions of the etched/regrown devices persist over a greater current range and exhibit maximum output powers larger than air-post lasers. The lasers are anisotropically etched into the lower monolithic distributed Bragg reflector using an electron cyclotron resonance SiCl₄ plasma etch. After transfer in ultra-high vacuum, epitaxial AlGaAs current blocking layers are regrown around the etched mesas. Polycrystalline deposition on the SiO₂ mask is removed by reactive ion etching to allow electrical contact and top surface emission. The etched/regrown laser characteristics demonstrate efficient current confinement and low thermal impedance. The vacuum integrated processing described offers the prospect of further device performance enhancements and greater functionality     

High-power operation of an argon excimer laser with a MgF2 and SiC cavity

An intense coherent light pulse whose energy, height and width (FWHM) were 80 mJ, 16 MW, and 5 ns, respectively, was obtained as 126 nm from an argon excimer laser. A superpoished SiC mirror was used in combination with a MgF₂ output coupler for an electron-beam-pumped argon excimer laser. The SiC mirror had a reflectivity at 126 nm as high as 47% and was highly damage resistant. Laser mirror materials for high-power short-wavelength lasers are discussed. Surface damage on the MgF₂ output mirror could not be avoided; this prevented stable operation of the argon excimer laser. In order to obtain such high power from the argon excimer laser, it is necessary to construct the resonator without a MgF₂ coupler. An unstable resonator is considered as the best candidate for the stable operation of the argon excimer laser     

原子层沉积方法制备低温多层Al2O3/TiO2复合封装薄膜的研究

原子层沉积(ALD)方法可以制备出高质量薄膜,被认为是可应用于柔性有机电致发光器件(OLED)最有发展前景的薄膜封装技术之一。本文采用原子层沉积(ALD)技术,在低温(80℃)下,研究了Al₂O₃及TiO₂薄膜的生长规律,通过钙膜水汽透过率(WVTR)、薄膜接触角测试等手段,研究了不同堆叠结构的多层Al₂O₃/TiO₂复合封装薄膜的水汽阻隔特性,其中5 nm/5 nm×8 dyads(重复堆叠次数)的Al₂O₃/TiO₂叠层结构薄膜的WVTR达到2.1×10^-5 g/m²/day。采用优化后的Al₂O₃/TiO₂叠层结构薄膜对OLED器件进行封装,实验发现封装后的OLED器件在高温高湿条件下展现了较好的寿命特性。     

Reduction of current leakage in chemical-vapor deposited Ta2O5 thin-films by oxygen-radical annealing [DRAMdielectric]

The electrical properties of CVD-Ta₂O₅ thin-films are improved by post-deposition oxygen-radical annealing. Since this annealing is carried out at very low pressure (10^-6 torr), the growth of SiO₂ in Ta₂O ₅/Si interface is small, and the residual carbon in the film is reduced. The damage to the Ta₂O₅ film caused by oxygen ion bombardment is negligible, because few charged particles reach the film. A critical voltage V_crit of 1.45 V for the leakage current less than 10^-8 A/cm² was realized by these Ta₂O₅ films with the effective thickness t_eff of 2.59 nm. The V_crit value for oxygen-radical annealing is higher than that for oxygen-plasma annealing     

Low Dit, thermodynamically stable Ga2O3-GaAs interfaces: fabrication, characterization, and modeling

Thermodynamically stable, low D_it amorphous Ga₂ O₃-(100) GaAs interfaces have been fabricated by extending molecular beam epitaxy (MBE) related techniques. We have investigated both in situ and ex situ Ga₂O₃ deposition schemes utilizing molecular beams of gallium oxide. The in situ technique employs Ga₂O₃ deposition on freshly grown, atomically ordered (100) GaAs epitaxial films in ultrahigh vacuum (UHV); the ex situ approach is based on thermal desorption of native GaAs oxides in UHV prior to Ga₂O₃ deposition. Unique electronic interface properties have been demonstrated for in situ fabricated Ga₂O₃-GaAs interfaces including a midgap interface state density D_it in the low 10¹⁰ cm^-2 eV^-1 range and an interface recombination velocity S of 4000 cm/s. The existence of strong inversion in both n- and p-type GaAs has been clearly established. We will also discuss the excellent thermodynamic and photochemical interface stability. Ex situ fabricated Ga₂O₃-GaAs interfaces are inferior but still of a high quality with S=9000 cm/s and a corresponding D_it in the upper 10¹⁰ cm^-2 eV^-1 range. We also developed a new numerical heterostructure model for the evaluation of capacitance-voltage (C-V), conductance-voltage (G-V), and photoluminescence (PL) data. The model involves selfconsistent interface analysis of electrical and optoelectronic measurement data and is tailored to the specifics of GaAs such as band-to-band luminescence and long minority carrier response time τ_R. We will further discuss equivalent circuits in strong inversion considering minority carrier generation using low-intensity light illumination     

Semiconductor lasers with 2-D-photonic crystal mirrors based on awet-oxidized Al2O3-mask

We have fabricated and investigated AlGaAs-InGaAs-based ridge waveguide (RWG) lasers with two-dimensional (2-D) triangular photonic crystal (PC) mirrors using a wet-oxidized Al₂O₃ mask for the dry etching of the PC at one end of the ridge. The laser structure includes a 60-nm-thick AlAs layer positioned in the upper cladding, which is converted into Al₂O₃ after the definition of the PC by electron beam lithography and shallow etching. Etching of the holes is then continued using the Al₂O₃ mask, to a final depth of 600 nm. The continuous-wave characteristics of the lasers show a clear dependence on the period of the PC including a significant decrease of the threshold current and an increase of the efficiency for properly adjusted crystal parameters     

Surface passivation of GaAs MESFETs

The metal semiconductor field effect transistor (MESFET) represents a more realistic test for “passivation” efficacy than conventional capacitor test structures due to its prototypical fabrication process. This paper evaluates Gallium-Arsenide (GaAs) surface passivation films utilizing the MESFET as a test vehicle. For this study, gate-to-drain leakage current, gate-to-drain breakdown voltage, complex impedance versus frequency, and low-frequency noise measurements are performed on MESFETs with various passivation films. The results indicate that a hydrogen plasma used to “pre-clean” the GaAs surface in conjunction with an in situ plasma-enhanced chemical vapor deposition (PECVD) Si₃N₄ passivation film yields the best performance. In contrast, atomic-layer-epitaxial ZnSe demonstrated inferior performance (even in comparison to PECVD Si₃N₄ passivation films that did not receive a hydrogen “pre-clean”)     

End-pumped Nd:LaF3 and Nd:LaMgAl11O19 lasers

Nd:LaF₃ and Nd:LaMgAl₁₁O₁₉ (LMA) are promising candidates for pulsed diode-laser-pumped lasers because they have relatively long upper state lifetimes and large absorption bandwidths compared to other Nd³⁺ doped materials. Crystal growth of LMA and the spectroscopic properties of both materials are described. Continuous-wave (CW) end-pumped lasers have been demonstrated in these materials using a Ti:Al₂O₃ laser to simulate the diode-laser pump source. Slope efficiencies of 47% for Nd:LaF₃ and 32% for Nd:LMA were obtained. The results for Nd:LaF₃ are typical for end-pumped, CW, Nd³⁺ lasers; the lower slope efficiency for Nd:LMA is attributed to excited-state absorption     

Nd:Y2O3透明陶瓷4F3/2-4I11/2跃迁光谱及高效激光输出

报道了采用真空烧结法结合热等静压技术制备的Nd:Y₂O₃透明陶瓷的荧光光谱特性及相关激光输出。通过与Nd:YAG透明陶瓷的荧光光谱对比,表明Nd:Y₂O₃透明陶瓷的4F_3/2-4I_11/2跃迁光谱存在着多个增益相当的谱线,这更有利于实现同时双波长段激光振荡;不同斯塔克子跃迁光谱的离散特性有利于通过腔镜镀膜控制不同波长损耗,获得丰富的1.0~1.1 μm波段激光。利用简单的平平两镜腔结构完成进一步的实验,通过选择的输出镜片镀膜获得了输出功率3.62 W、转换效率40.4%的1074.6 nm和1078.8 nm的双波长输出和输出功率1.7 W、转换效率19.4%的1130.3 nm波长输出。     

Plasma-Enhanced Atomic Layer Deposition of Amorphous Ga2O3 for Solar-Blind Photodetection

Wide-bandgap gallium oxide(Ga₂O₃) is one of the most promising semiconductor materials for solar-blind(200 nm to 280 nm) photodetection. In its amorphous form, amorphous gallium oxide(a-Ga₂O₃) maintains its intrinsic optoelectronic properties while can be prepared at a low growth temperature, thus it is compatible with Si integrated circuits(ICs) technology. Herein, the a-Ga₂O₃ film is directly deposited on pre-fabricated Au inter...     

Characterizing Fluorine-Ion Implant Effects on Poly-Si Thin-Film Transistors With ${hbox{Pr}}_{2}{hbox{O}}_{3}$ Gate Dielectric

The fluorine ion implantation applied to the polycrystalline silicon thin-film transistors (poly-Si TFTs) with high-k Pr₂O₃ as gate dielectric is investigated for the first time. Using the Pr₂O₃ gate dielectric can obtain a high gate capacitance density and thin equivalent-oxide thickness, exhibiting a greatly enhancement in the driving capability of TFT device. Introducing fluorine ions into the poly-Si film by fluorine ion implantation technique can effectively passivate the trap states in the poly-Si film and at the Pr₂O₃/poly-Si interface to improve the device electrical properties. The Pr₂O₃ TFTs fabricated on fluorine-implanted poly-Si film exhibit significantly improved electrical performances, including lower threshold voltage, steeper subthreshold swing, higher field-effect mobility, lower off-state leakage current, and higher on/off current ratio, as compared with the control poly-Si Pr₂O₃ TFTs. Also, the incorporation of fluorine ions also improves the reliability of poly-Si Pr₂O₃ TFTs against hot-carrier stressing, which is attributed to the formation of stronger Si-F bonds. Furthermore, superior threshold-voltage rolloff characteristic is also demonstrated in the fluorine-implanted poly-Si Pr₂O₃ TFTs. Therefore, the proposed scheme is a promising technology for high-performance and high-reliability solid-phase crystallized poly-Si TFT.     

Plasma charging damage on MOS devices with gate insulator ofhigh-dielectric constant material

Plasma charging effects on the gate insulator of high-dielectric constant (k) material in MOS devices deserve to be investigated because of different trap-assisted conduction mechanisms. Plasma-induced degradation in gate-leakage current and time to breakdown is clearly observed in this work. MOS device with Si₃N₄ film seems to have smaller degradation of gate-leakage current while it suffers shorter time to breakdown as compared to Ta₂O₅ samples. For devices with Ta₂O₅ film, a larger physical thickness suffers more reliability degradation from plasma charging damage because of the richer traps. Thus, a smaller physical thickness of high-k dielectric film is favorable for sub-micron MOS devices of ULSI application     

High-performance polycrystalline SiGe thin-film transistors usingAl2O3 gate insulators

The use of aluminum oxide as the gate insulator for low temperature (600°C) polycrystalline SiGe thin-film transistors (TFTs) has been studied. The aluminum oxide was sputtered from a pure aluminum target using a reactive N₂O plasma. The composition of the deposited aluminum oxide was found to be almost stoichiometric (i.e., Al₂O₃), with a very small fraction of nitrogen incorporation. Even without any hydrogen passivation, good TFT performance was measured an devices with 50-nm-thick Al₂O₃ gate dielectric layers. Typically, a field effect mobility of 47 cm²/Vs, a threshold voltage of 3 V, a subthreshold slope of 0.44 V/decade, and an on/off ratio above 3×10⁵ at a drain voltage of 0.1 V can be obtained. These results indicate that the direct interface between the Al₂ O₃ and the SiGe channel layer is sufficiently passivated to make Al₂O₃ a better alternative to grown or deposited SiO₂ for SiGe field effect devices     

Optimization of fluorine passivation of stainless steel surfaces

The optimum conditions for the fluorine passivation of 316L stainless steel are described. The direct fluoridation products formed at temperatures of 320°C or lower are composed solely of FeF₂ , while those which were formed at the temperatures of 330°C or higher have a compound-phase composition of FeF₂ and FeF ₃. At a critical temperature (400°C for 316L stainless steel) of the thermal modification process, FeF₃ is converted to FeF₂ and disappears completely as the temperature rises. Meanwhile, CrF₃ is formed at a certain temperature (440°C for 316L stainless steel). The two-phase composition gets further crystallized as the thermal modification temperature rises. As the crystal growth induces the cracks on the fluoridated film, it is very difficult to form a satisfactory passivation film from the two-phase composition by thermal modification. It is confirmed that excellent passivation film has been obtained from the single-phase composition by the optimum fluoridation following the optimum thermal modification     

Ion milling properties of laterally emitting thin-filmelectroluminescent materials

A study has been undertaken of the ion milling properties of ZnS:Mn, Y₂O₃, Si₃N₄, SiO₂, SiO_xN_y, and Al versus the etching time, the acceleration voltage, and the angle of incidence of the ion beam. Different ZnS:Mn etched profiles have been fabricated by modifying the angle of incidence; these are in agreement with the reported simulations