Dry-etched 650 nm AlGaInP visible-light laser diodes with operatingtime of over 3000 h

The authors have achieved CW operation of 650 nm GaInP/AlGaInP index waveguide-type visible-light laser diodes (LDs) with dry-etched mesa stripes fabricated by Cl₂ reactive ion beam etching. The threshold current of 47 mA and slope efficiency of 0.40 W/A are almost the same as those of a wet-etched LD fabricated from the same wafer (L=500 μm). The cross-sectional scanning electron microscope view of the buried mesa stripe shows that the dry-etched LD has a symmetric mesa shape resulting in a small focusing spot and stable mode operation. The wet-etched mesa, however, is asymmetric because a 6° misoriented substrate is used for this wavelength operation. An aging test with light output power of 3 mW at 50°C has revealed that these LDs have an operating time of over 3000 h, which represents a sufficient reliability for conventional uses     

Selective growth of InP on patterned,nonplanar InP substrates by low-pressure organometallic vapor phase epitaxy

The effects of indium sources, mask materials and etched mesa profiles on growth mor-phology of Fe-doped semi-insulating InP on patterned, nonplanar InP substrates were studied for low-pressure organometallic vapor phase epitaxy (OMVPE). The presence or absence of polycrystalline InP layers deposited on the mask was found to depend on the indium source but not on the mask material. Trimethylindium was found to be the preferable indium source for prevention of polycrystalline InP deposits on the mask. The etched mesa shape was found to dominate the final geometry of the OMVPE re-grown InP layer. Inclusion of an interfacial layer of 1.16 μm bandgap wavelength InGaAsP between the dielectric mask and InP substrate produces a favorable mesa shape by con-trolling the level of undercut during mesa etching, so as to form a smooth mesa profile. After selective regrowth of InP over the resulting mesa, a planar surface is typically achieved for mesa stripes with a mask overhang length as long as 2.6 μm and a mesa height as high as 4 μm.     

Effect of Mesa Size on Thermal Characteristics of Vertical-cavity Surface-emitting Lasers

The effect of mesa size on the thermal characteristics of etched mesa vertical-cavity surfaceemitting lasers（VCSELs） is studied. The numerical results show that the mesa size of the top mirror strongly influences the temperature distribution inside the etched mesa VCSEL. Under a certain driving voltage, with decreasing mesa size, the location of the maximal temperature moves towards the p-contact metal, the temperature in the core region of the active layer rises greatly, and the thermal characteristics of the etched mesa VCSELs will deteriorate.     

InSb阵列探测芯片的感应耦合等离子反应刻蚀研究

利用感应耦合等离子（ICP）反应刻蚀（RIE）进行了InSb阵列芯片台面刻蚀,并利用轮廓仪、SEM及XRD对台面形貌以及刻蚀损伤进行分析。采用优化的ICP刻蚀参数,实现的刻蚀速率为70~90 nm/min,刻蚀台阶垂直度~80°,刻蚀表面平整光滑、损伤低。与常规的湿法腐蚀相比,明显降低了侧向钻蚀。台面采用此反应刻蚀工艺,制备了具有理想I-V特性的320×256 InSb探测阵列芯片,在-500 mV到零偏压范围内,光敏元（面积23 μm×23 μm）的动态阻抗（Rd）大于100 MΩ。     

LBIC技术研究InGaAs线列探测器串音及光敏感区

利用激光诱导电流技术研究了InGaAs台面探测器的相邻探测器间的串音和光敏感区。用分子束外延方法生长掺杂InGaAs的PIN InP/InGaAs/InP 外延材料,制备了256×1正照射台面InGaAs线列探测器。测试结果表明,InGaAs线列探测器相邻探测器间没有串音,虽然台面结构周围吸收层已被腐蚀,但因为少数载流子的侧向收集,扩大了有效光敏感区。     

Selective growth of InP by MOCVD around dry-etched mesas having various patterns for photonic integrated circuits

We have investigated the selective growth ofpnp- InP by metalorganic chemical vapor deposition (MOCVD) around mesas. The mesas were formed by reactiveion-etching using SiO₂ masks having various patterns. The patterns include stripes along different crystallographic orientations, Y-bifurcations, and X-crossings. The behavior of the growth, and that of the mass transport before the growth, were found to depend remarkably on the crystallographic direction of the mesa stripe. The most notable mass transport, which transforms a nearly vertical mesa wall to a sloped one, was observed for a stripe misoriented by about 30° from the [011] direction. The growth was observed to proceed preferentially on the sloped planes, planarizing the crystal surface, for a mesa stripe directed between the [011] and [010] directions. However, for the stripe direction near [01-1], the growth was observed to creep up a nearly vertical plane on the mesa wall, and sloped planes are reluctant to form. Selective growth with sufficient planarity has been obtained for various waveguides including the Y-bifurcations and the X-crossings, which are used as the waveguide components in photonic integrated circuits, when the stripes are almost along the [011] direction.     

Embedded-stripe GaAs-GaAlAs double-heterostructure lasers with polycrystalline GaAsP layers--II: Lasers with etched mirrors

Monolithic CW lasers with low threshold are reported in which mesa stripes are embedded with vapor-phase-grown high-resistivity GaAsP layers and cavity mirrors are formed by chemical etching. An etching solution consisting of NaOH, H2O2, and NH4OH has turned out to offer excellently flat-cavity mirrors on     

Analysis of InP Regrowth on Deep-Etched Mesas and Structural Characterization for Buried-Heterostructure Quantum Cascade Lasers

We investigated the effect of deep-etched mesa sidewall profile and oxide overhang length on the regrowth structural characteristics for buried- heterostructure (BH) quantum cascade lasers (QCLs) grown by metalorganic chemical vapor deposition (MOCVD). The relationship between etched mesa sidewall geometry, oxide overhang length, oxide thickness, and growth uniformity was examined and is extensively discussed. In particular, anomalous growth in the vicinity of the oxide edge resulting from insufficient oxide overhang length was identified and studied. An ideal ratio of mesa height to oxide overhang length between 2.5 and 3.0 is proposed and experimentally justified to yield satisfactory planar regrowths without anomalous growth. Mesas in the [ 0 1[` 1] ] [ 0 1\overline{ 1} ] direction with smoothly etched entrant profile yield a higher degree of growth uniformity than mesas in the [011] direction with the re-entrant profile.     

Orientation dependentp-type conversion of Fe:InP in hydride VPE regrown EMBH lasers

We have studied semi-insulating Fe:InP regrowth of etched mesa buried heterostruc-ture lasers by hydride vapor phase epitaxy. Type-sensitive staining and electron beam induced current photographs have shown that regions near the original etched mesa are p-type instead of semi-insulating in a number of our wafers. These regions begin and end on distinct crystal boundaries, indicating that thep-type conversion is not due to simple diffusion of Zn out of the laser base structure, but is associated with uncontrolled growth of {111}_In crystal planes.     

(Al)GaInP laser with lateral confinement by epitaxial growth onnonplanar substrates

The authors present an AlGaInP/GaInP strained QW laser with AlGaAs cladding layers grown over nonplanar substrates. Excellent device quality and performance is obtained on substrates patterned with ridges prior to epitaxial growth. The lateral current and carrier confinement achieved by exploiting the disordering of the neutral superlattice at ridge sidewalls with shallow angles results in a threshold current density for 5-μm-wide stripes that is one-half that of conventional devices. The potential of this device for high electrical-to-optical conversion makes it well suited for applications to dense addressable laser arrays     

Maskless Lateral Epitaxial Growth of Gallium Nitride Using Dimethylhydrazine as a Nitrogen Precursor

Lateral epitaxial growth (LEG) is a key technology to improve the lifetime of III-V nitride-based laser diodes (LDs) by reducing the dislocation density in the materials. To increase the area of low dislocation density, the lateral growth rate needs to be increased. In addition, suppression of the vertical growth is strongly desired to avoid unnecessarily thick growth, which would result in cracks in the epitaxial film. This paper reports the maskless LEG of GaN with extremely high lateral-to-vertical growth rate ratio using dimethylhydrazine as a nitrogen precursor. The lateral growth only occurs from the sidewalls of the etched mesa stripes without any dielectric masks. The lateral growth rate toward the direction is extremely high, as high as 10 μm/h, while no vertical growth is observed on the top of unmasked mesa. The cross-sectional transmission electron microscopic image shows that the threading dislocations in the wing region extend only toward the lateral direction. Note that almost smooth coalescence between the wing regions is confirmed by atomic force microscopy. X-ray diffraction measurements reveal that this maskless LEG drastically improves the crystallographic twist down to 97 arc-s, which is as comparably low as that of a free-standing GaN substrate. The presented maskless LEG is advantageous for optical device applications.     

Localized deposition of GaAs/GaInP heterostructures using LP-MOVPE

GaInP layers were grown selectively by low pressure MOVPE in patterned SiO₂ masks on GaAs (100) substrates. The variation of the composition and spontaneous ordering phenomena were analysed by Raman spectroscopy and photoluminescence. In contrast to GaInAs, the composition of GalnP shows only a very weak dependence on the size of the structures. On the other hand, there is a shift of the bandgap energy up to 40 meV with decreasing size of the stripes caused by ordering of the Ga and In atoms. Based on these findings lattice matched GaAs/GalnP multilayers were grown to delineate the growth history of the structures. It was demonstrated that the growth habit of deposition in narrow slits (>1μm) can be used to produce mesa-like stripes with dimensions below 100 nm on top of the mesa. Results of GaAs/GaInP quantum wells selectively grown on top of a mesa are presented.     

Single mode operation of buried heterostructure lasers by loss stabilization

A loss-stabilized buried heterostructure (LSBH) laser is reported that is much simpler to grow than conventional BH lasers, but has similar, near ideal, laser characteristics. Typical lasers, which incorporate an optical guide have active stripe widthsapprox 2.5 mum determined by the initial mesa etching, have a laser threshold of 25 mA, and exhibit stable single transverse mode operations up to 60 mA and higher currents. The simplicity in growth results from not attempting to grow a single mode guide by carefully choosing the composition of the regrown burying layers, but instead simply forming a multiple mode guide by growing a cladding layer with a high aluminum composition. The large index discontinuity between the layer and the central mesa and the roughness of the etched mesa walls cause losses when interface scattering couples light from the initial mode into other modes. The losses rapidly increase with the mode number and, we believe, provide the selection mechanism which causes the laser to operate in the lowest mode. Calculations show that the observed variations in mesa width of 0.3 μm over distances of 10μm are adequate to explain the observed lowest mode stability.     

Cl2/Ar/BCl3 ICP刻蚀对AlGaN的损伤研究

感应耦合等离子体(ICP)刻蚀在AlGaN基紫外探测器台面制作中起着重要作用,初步研究了Cl2/Ar/BCl3ICP刻蚀对AlGaN材料的损伤。运用X射线光电子能谱(XPS)对ICP刻蚀前后的n型Al0.45Ga0.55N表面进行了分析,并对刻蚀后AlGaN材料在N2气中快速热退火进行了研究。结果表明,在N2气中550°C退火3 min对材料的电学性能有明显的改善作用。     

Performance and Reliability of 12.5-Gb/s Oxide-Free 850-nm Mesa VCSELs

Oxide-free mesa vertical-cavity surface-emitting lasers (VCSELs) emitting at 850 nm have been designed for short reach datacom applications at data rates up to 12.5 Gb/s. The top distributed Bragg reflector is etched away creating a mesa that provides both current and photon confinement. The devices exhibit low threshold current and a donut-shaped far-field profile that is suited for transmission on both legacy and laser-optimized multimode fibers. Open eye diagrams with high margin are observed in on-wafer testing of 8-10 mum VCSELs at 10.3125 Gb/s over 5degC-95degC. Accelerated aging tests indicate a long device lifetime, with the time for a cumulative failure of 1% estimated to be 15 million h at 40degC for 12-mum VCSELs.     

Type-II interband cascade lasers in the 4.3-4.7-/spl mu/m wavelength region

Operation of type-II interband cascade lasers in the 4.3-4.7-/spl mu/m wavelength region has been demonstrated at temperatures up to 240 K in pulsed mode. These lasers fabricated with 150-/spl mu/m-wide mesa stripes operated in continuous-wave (CW) mode up to a maximum temperature of 110 K, with an output power exceeding 30 mW/f and a threshold current density of about 41 A/cm/sup 2/ at 90 K. The maximum CW operation temperature of 110 K is largely limited by the high specific thermal resistance of the 150-/spl mu/m-wide broad area lasers. A 20-/spl mu/m-wide mesa stripe laser was able to operate in CW mode at higher temperatures up to 125 K as a result of the reduced specific thermal resistance of a smaller device.     

台面尺寸对垂直腔面发射激光器电学特性的影响

采用求泊松方程、电流密度方程、载流子扩散方程以及有源层结压降方程自洽解的方法,计算了不同台面大小的台面结构垂直腔面发射激光器内部的电势分布和有源层中的注入电流密度、载流子浓度及结压降分布.结果表明,台面尺寸对垂直腔面发射激光器内部的电势分布和有源层中的注入电流密度、载流子浓度及结压降分布有重要影响.在一定的外加电压下,随着台面尺寸减小,有源层中心处的注入电流密度、载流子浓度和结压降急剧减小,垂直腔面发射激光器性能恶化.     

Lithium Niobate Ridge Waveguides Fabricated by Wet Etching

The fabrication of LiNbO₃ ridge waveguides etched by a mixture of HF and HNO₃ using chromium (Cr) stripes as masks is reported. Smooth etched surfaces are obtained by adding some ethanol into the etchant. Under-etching is nearly avoided by annealing the sample with the Cr masks before the wet etching process. Low-loss monomode ridge guides with a height of up to 8 mum and a width between 4.5 and 7.0 mum are demonstrated. As an example, the propagation losses in a 6.5-mum-wide and 8-mum-high structure are 0.3 dB/cm for transverse-electric and 0.9 dB/cm for transverse-magnetic polarization, respectively, at 1.55-mum wavelength     

Effective screen for fast aging InGaAsP BH lasers using electrical derivatives

We report here the first use of electrical derivatives to predict threshold current degradation rates for InGaAsP, etched mesa BH lasers. Fast aging lasers are found to display a post-threshold I dV/dI temperature dependence which sets them apart from slow agers. This signature is explained in terms of a nonlinear current leakage path in the confinement layers. We propose the use of the I dV/dI temperature signature as a screen to eliminate fast aging lasers in high-reliability applications.     

Improved light extraction of wafer-bonded AIGaInP LEDs by surface roughening

By using the wafer bonding technique and wet etching process, a wafer bonded thin film AlGaInP LED with wet etched n-AlGaInP surfaces was fabricated. The morphology of the etched surface exhibits a pyramid-like feature. The wafer was cut into 270× 270 μm2 chips and then packaged into TO-18 without epoxy resin. With 20-mA current injection, the light intensity and output power of LED-I with surface roughening respectively reach 315 mcd and 4.622 mW, which was 1.7 times higher than that of LED-II without surface roughening. The enhancement of output power in LED-I can be attributed to the pyramid-like surface, which not only reduces the total internal reflection at the semiconductor-air interface but also effectively guides more photons into the escape angle for emission from the LED device.