SEM direct observation of the degradation in Ga(Al)As GRIN-SCH lasers grown on a silicon substrate

The starting of the degradation in GRIN-SCH GaAs lasers grown on a silicon substrate was directly observed by EBIC and CL techniques. The investigation of electron beam induced damage shows that the degradation of these devices starts in the p-n junction before it attains the active layer and before the appearance of dark line defects.<>     

大功率量子阱远结半导体激光器

通过将下波导层掺杂为ｐ型,使半导体激光器的有源区与ｐｎ结分离,制作了大功率远结半导体激光器。该器件在老化期间表现出输出功率变大的趋势。理论分析表明,远结半导体激光器特殊的外延结构,决定了器件的阈值比正常器件的高,但是阈值受温度的影响较小,并且器件的退化机制转变为ｐｎ结的退化,这对于制作高可靠性、长寿命、低温度敏感性的半导体激光器具有重要意义。     

Oxide defined TJS lasers in InGaAsP/InP DH structures

Transverse junction stripe lasers in the InGaAsP-InP systems have been fabricated by Zn diffusion through oxide windows into DH structures of InGaAsP/InP with all epitaxial layers n-type. The quaternary layer composition is such that room temperature laser emission is at 1.18 μm. TJS laser mode behavior with accompanying single longitudinal mode operation and kink-free light-output characteristics are seen at 77 K. As the temperature is increased, this behavior persists up to about 130 K, when parallel electron injection through the p-n junction in the InP layers becomes so large that, in parallel with the TJS laser filament, a normally operating DH laser filament starts operating. At higher temperatures only the latter is seen to operate.     

Degradation Mode Analysis on Highly Reliable Guardring-Free Planar InAlAs Avalanche Photodiodes

This paper presents the high reliability of the guardring-free planar InAlAs avalanche photodiode (APD) and its degradation mode analysis. We have conducted long-term and high-temperature aging tests under 175degC, 200degC, 225degC, and 250degC. There were three degradation modes as follows: 1) the increase in the dark current; 2) the decrease in the breakdown voltage; and 3) short circuit. Their thermal activation energies were 0.96, 1.30, and 0.93 eV, respectively. Their estimated mean times to failures at 85 are 25, 100, and 22 million hours, respectively. Increased dark current is generated in the upper side of the absorbing layer. The breakdown voltage decreased with aging time because the depletion width in the absorbing layer shrinks from the region side. Any degradation mode on the surfaced p-n junction did not appear in spite of the 10 000-h aging test at a high temperature of 200degC. The guardring-free planar InAlAs APD has the advantage of high reliability because the electric field of a surfaced p-n junction is weakened by the underlying field control layer.     

Modeling the defect distribution and degradation of ultrathin CdTe films

The defect distribution across an ultrathin film Cd Te layer of a Cd S/Cd Te solar cell is modelled by solving the balance equation in steady state. The degradation of the device parameters due to the induced defects during ion implantation is considered where the degradation rate is accelerated if the defect distribution is considerable.The defect concentration is maximum at the surface of the Cd Te layer where implantation is applied and it is minimum at the junction with the Cd S layer. It shows that ultrathin devices degrade faster if the defect concentration is high at the junction rather than the back region(Cd Te/Metal). Since the front and back contacts of the device are close in ultrathin films and the electric field is strong to drive the defects into the junction, the p-doping process might be precisely controlled during ion implantation. The modeling results presented here are in agreement with the few available experimental reports in literature about the degradation and defect configuration of the ultrathin Cd Te films.     

Avalanche breakdown characteristics of a diffused P-N junction

A one-dimensional analysis is presented on the avalanche breakdown characteristics of a diffused p-n junction diode. By numerically integrating the carrier ionization rate in a junction space-charge layer, avalanche breakdown voltage is calculated for diffused diodes of silicon and germanium; this voltage is graphically illustrated throughout a range of parameters applicable to most practical situations. In addition, for calculating the maximum cutoff frequency of varactor diodes, junction capacity is similarly illustrated assuming the device is biased to avalanche breakdown. From these illustrations, and from an accompanying nomograph which relates the physical constants of a junction to its impurity atom gradient, the above parameters can be readily established without additional calculations. Further, examples are also presented to demonstrate the reduction of breakdown voltage resulting from a rapid increase of conductivity within the space-charge layer of a diffused p-n junction; this situation approximates many epitaxial and double diffused structures.     

Optical field distribution in close-confined laser structures

An experimental and theoretical study has been made of the radiation patterns from GaAs lasers with a "close-confined" structure. The lasers were grown by liquid-phase epitaxy and consisted of a p+ - p-n structure with Al in the p+ region. Photometric measurements were made of the intensity distribution at the emitting facet (microscope observations) and the radiation pattern in a plane perpendicular to the junction. The electromagnetic field distribution in the vicinity of the p-n junction and the radiation pattern were calculated by solving the wave equation for a three-layer structure with complex dielectric constants in each layer. The theory predicts enhanced confinement of the radiation by the increased dielectric discontinuity due to the heterojunction, in agreement with the low lasing threshold and high efficiencies of the close-confined diodes. Another consequence of the theory is that as the thicknessdof thepregion of the cavity is increased, higher order modes can propagate with efficiences much greater than in ordinary lasers without the heterojunction. The third mode, corresponding to three intensity maxima along a line perpendicular to the junction, was observed ford = 5 mu. The good agreement found between the observed and calculated radiation patterns indicates that confinement of the radiation by dielectric discontinuities is an important factor in explaining the low-threshold currents found in close-confined lasers.     

Analysis of gain-induced waveguiding in stripe geometry diode lasers

This paper analyzes two-dimensional waveguiding in stripe geometry diode lasers. Refractive index discontinuities guide the light by total internal reflection in the direction perpendicular to the p-n junction plane, but the guidance mechanism along the p-n junction and transverse to the propagation direction is that of gain variation. In the active region, the gain is a maximum under the pump stripe center and decreases to loss (optical absorption) in the unpumped region. This variation is modeled by three different functions for which analytic solutions are obtained. The first is the usual quadratic. The second, by choice of parameters, represents transition cases from quadratic to square gain profiles, which occur with increasing stripe width. The third is quadratic near stripe center and continuously decreases to a constant loss value in the unpumped region. We present mode patterns, laser threshold gains, and propagation constants for a variety of cases to illustrate the effects of laser length, stripe width, and active region thickness in these devices.     

InGaAsP/InP平面条形双异质结激光器结构参数对阈值电流密度的影响

平面条形双异质结激光器的模式和阈值电流特性可以用两维波导模型来分析.本文从解场方程出发,求出波导的模式.并从模式宽度与增益之间的关系,以及阈值条件,求出阈值电流密度相应于各种参数,特别是相应于有源层厚度和条宽的解析表式达.     

A groove GaInAsP laser on semi-insulating InP using a laterally diffused junction

Low threshold current GaInAsP/InP groove lasers have been fabricated on semi-insulating InP substrates. Three n-type layers are grown with a single liquid phase epitaxial (LPE) growth process, and the p-n junction is formed by a lateral Zn diffusion. The active layer inside the groove provides a real index waveguide. Threshold currents as low as 14 mA with 300 μm cavity length are obtained. A single longitudinal mode at 1.3 μm up to1.4 I_{TH}is observed. The lasers operate with a single lateral mode when the active region width is less than 2.5 μm. This laser is suitable for monolithic integration with other optoelectronic devices.     

Comparison of the aging behavior of diffused and epitaxial GaAlAs heterojunction electroluminescent diodes

Two Types of GaAlAs heterojunction electroluminescent diodes are compared. In the planar-type diffused diode the p-n homojunction is obtained by zinc diffusion in areas limited by a silicon nitride mask; the p-p heterojunction confines electrons in the bulk and avoids surface recombinations. The epitaxial diode is a conventional double heterojunction; the active area is limited by proton bombardment. The aging behaviors of these two types appear quite different. Diffused diodes degrade relatively fast; under continuous operation at 550 A/cm²(100 mA) the device lifetime (emitted light power falling down to 50 percent of the initial value) is 10 000 to 50 000 h. Epitaxial diodes degrade much more slowly; their device lifetime is estimated at several 10⁵h. The degradation is followed during aging, by using electrical and optical measurements, together with SEM and TEM analyses. It is confirmed that fast degradation occurs with simultaneous growth of dark line defects (DLD) and that these DLD's result from dislocation dipoles of interstitial nature, emitted either from scratches or, more frequently, from previously existing dislocations. It is shown that epitaxial diodes are practically free of dislocations; on the contrary, in the case of planar-type p-n junctions, a large number of dislocation loops are developed at the junction periphery, resulting from the mechanical stress at the edge of the junction during processing. This is the main source of DLD's and fast degradation of planar-type diffused diodes.     

半导体激光器的主要失效机理及其与芯片烧结工艺的相关性

分析了GaAs/CaAlAs高功率半导体激光器的暗线缺陷，腔面损伤退化和电极退化等主要失效机理及主要失效模式。通过样品老化试验，从微观物理角度分析了光功率输出下降与芯片烧结工艺相关性，明确了烧结焊料引起PN结短路，烧结空隙，焊料沾污等是导致半导体激光器退化的一个主要因素。     

New structures of GaAlAs lateral-injection laser for low-threshold and single-mode operation

Two new structures of lateral-injection transverse junction stripe (TJS) lasers, in which the stripe geometry is formed by the double heterojunctions, have been developed. These lasers, the homojunction type and the single-heterojunction type, have a self-reverse-biased p-n junction for concentrating current into the narrow active region. The temperature dependence of the threshold current has been very much improved in one of the new structures, the homojunction type, and is fair compared with those of good conventional broad-contact lasers. The threshold current does not increase rapidly up to 350 K in the homojunction lasers. These lasers exhibit improved characteristics of low threshold, the single longitudinal mode oscillation as well as the single fundamental transverse-mode oscillation, and "kink-free" behavior in the current depedence of the light-output power.     

Novel Hg<Subscript>x</Subscript>Cd<Subscript>1−x</Subscript>Te device structure for higher operating temperature detectors

A novel detector structure in which photons are absorbed in narrow-gap material, but the junction lies in wider bandgap material, has been examined. A possible reduction in bulk 1/f noise by a factor of 33 for a 240 K operation was predicted, based on studies that have suggested that the source of 1/f noise is the p-n junction and the large reduction in 1/f noise, which is observed in conventional detectors when the bandgap is increased. The increased bandgap at the junction produces a potential barrier; however, calculations are presented showing that for T > 150 K the thermal energy of the electrons enables them to cross the barrier and reach the p-n junction before recombining in the active region, thus giving high quantum efficiency. Experiments performed on the diodes showed that the quantum efficiency was maintained as expected, but the 1/f noise was not reduced, suggesting that it does not originate at the p-n junction. However, the structure does give excellent reverse-bias characteristics with low breakdown even at 2-V reverse bias.     

An electrical model with junction temperature for light-emitting diodes and the impact on conversion efficiency

We present an electrical model for quantum-well light-emitting diodes (LEDs) with a current-spreading layer. The LEDs studied have a multiquantum well (MQW) between p-GaN and the n-GaN grown on sapphire. The model consists of a diode connected with a series resistor resulting from the combined resistance of the p-n junction, contacts, and current spreader. Based upon this model, the I-V curve of the diode itself without the series resistance is extracted from the measured LED I-V curve. The model also includes an empirical diode current equation which was sought by matching the extracted I-V curve. In the seeking process, junction temperature (T/sub j/) rather than case temperature (T/sub c/) was used in the equation. The diode model allows one to calculate the reduction on conversion efficiency caused by the series resistor. Results show that the current-spreading layer causes 20% of the efficiency reduction at T/sub j/=107/spl deg/C.     

Correlation of emission and electrical properties of gallium arsenide transistor structures

Transistor structures were fabricated in si-doped solution, grown GaAs. The p-n junction used as anl emitter was formed during the growth of the epitaxial layer employing amphoteric Si doping. The collector junction was made by a planar sulphur diffusion. The behavior of the emitted light and the collector current as a function of the emitter base current are observed. The degradation in quantum efficiency and transistor alpha is noted to be due to the same diode current component. The degradation of alpha due to emitter crowding at high current levels is directly exhibited.     

Comparison between lasers isolated by oxygen implantation and SiO2isolated stripe lasers

GaAs/GaAlAs DH lasers isolated by an SiO2layer on top of the p-contacting layer are compared to DH lasers in which the isolation is maintained by an isolating the O+ -implanted layer within the n+- substrate. Measurements were performed on four O+ isolated lasers and five SiO2isolated lasers with the same composition and thickness of active and upper confinement layers. Threshold currents of both groups were very similar, whereas the O+ -implanted lasers showed superior thermal resistances by a factor of 2. Thermal resistances were measured by the shift of the lasing spectra with power dissipation.     

Self-consistent analysis of gain-guided triple stripe lasers

A considerable near field shift in DH triple stripe lasers is demonstrated by tailoring the applied bias on the stripes. No closed form solution for the current spreading in the passive layer is assumed. The two dimensional Laplace's equation in the passive layer, which is coupled with the diffusion equation of carriers in the active layer via the variation of the separation of quasi-Fermi levels, is solved consistently. Both the bimolecular and stimulated recombinations are included in the diffusion equation. The stimulated recombination determination couples the wave equation with the rest of the problem which is treated self-consistently. The paper highlights the influence of the different applied potentials on the stripes, the electrode spacing and the diffusion constant on the optical behaviour of the device.     

Characterization of excimer laser annealing of ion implanted Si

An evaluation of a XeCl excimer laser for the laser processing of Si is reported. The annealing quality of ion-implantation damage, as measured by the crystalline perfection of the regrown layer and by p-n junction characteristics, is similar to that obtained with ruby or Nd:YAG lasers. However, the wide energy window between annealing and surface damage, the flat smooth surface obtained after laser irradiation, the capability of providing deep surface melting, and other features, indicate that XeCl and perhaps other excimer lasers is nearly ideal for semiconductor processing.     

Threshold current reduction of GaInAs/GaInAsP/InP SCH quantum-welllasers with wire-like active region by using p-type substrates

The threshold current of GaInAs/GaInAsP/InP separate confinement heterostructure (SCH) quantum-well lasers with narrow (70-160-nm) wirelike active regions, which were fabricated by two-step LP-OMVPE growths and wet chemical etching, was much reduced (<1 kA/cm² ) by using p-type InP substrates. This result indicates the importance of eliminating the p-n junction from the regrowth interface to enhance injection of holes into the active region