Fabrication of V-grooved inner stripe GaAs-AlGaAs quantum-wire lasers

V-grooved inner stripe (VIS) GaAs-AlGaAs quantum-wire (QWR) lasers were successfully fabricated by, combining two-step metalorganic chemical vapor deposition (MOCVD) growth with a wet-etching technique. In order to achieve low threshold current density and high reliability, a conductive stripe width (W), a thickness (t/sub p-CBL/), and a doping concentration (n/sub p-CBL/) of the p-GaAs current-blocking layer (CBL) were determined to be W=1.2 /spl mu/m, t/sub p-CBL/=2 /spl mu/m, and n/sub p-CBL/=1/spl times/10/sup 18/ cm/sup -3/. The leakage currents passing through the CBL were also estimated using a modified P-SPICE. Thus far, a threshold current of 45 mA and an output power of 4 mW at 51 mA have been achieved under room-temperature pulsed operation for some devices with uncoated facets.     

A short-period GaAs-AlGaAs quantum-wire array laser with a submicrometer current blocking layer

The structure and device characteristics of a 700-nm-pitch GaAs-AlGaAs quantum-wire array laser (QWAL) with a dielectric defined current blocking layer are reported. The high wire density of the QWAL has been expected to yield more efficient carrier capture, but large spacing between the quantum wires was found to deteriorate the laser characteristics. In this work, we have improved electrical confinement into the active regions by incorporating a SiO/sub 2/ film onto the large spacing. Room-temperature pulsed operation with an output power of 9 mW at 191-mA injection current was achieved for a 200/spl times/500 /spl mu/m laser with uncoated facet. The threshold current density was 0.14 kA/cm/sup 2/. The dependence of the threshold current and the maximum power on the cavity length and width was also studied.     

Monolithic integration of GaAs-AlGaAs quantum-well lasers with directional couplers using vertical coupling of light

A novel technique for the monolithic integration of a laser and a directional coupler in the GaAs-AlGaAs material system is demonstrated. The combination of single-step molecular beam epitaxy (MBE) on a planar substrate, vertical coupling of light between the active and passive waveguide in a p-n-p-doped structure and the use of a self-aligned fabrication process for the ridge waveguides in the active and passive sections results in a threshold current of 52 mA and an output power of up to 0.6 mW. The directional coupler is completely switched at an applied bias of 4.0 V.     

Development of a large high-performance 2-D array of GaAs-AlGaAs multiple quantum-well modulators

We present the development of an ultrafast two-dimensional (288 /spl times/ 132 elements) reflection modulator array based on GaAs-AlGaAs multiple quantum-wells embedded in an asymmetric Fabry-Perot structure. The array has low operation voltage (< 4 V), low insertion loss, and high contrast ratio at /spl sim/846 nm. This array was hybridized to 0.25 /spl mu/m complementary metal-oxide-semiconductor driver providing 256 gray levels resolution at frame rate of 50 kHz (driver limited). Major progress in reducing the severe nonuniformity problem of the cavity resonance wavelength in such devices to less than 3.4 nm variation across a 4-in wafer was achieved.     

Fabrication of multiple wavelength lasers in GaAs-AlGaAs structuresusing a one-step spatially controlled quantum-well intermixing technique

We have applied a new technique, based on impurity-free vacancy diffusion, to control the degree of intermixing across a wafer. Bandgap tuned lasers were fabricated using this technique. Five distinguishable lasing wavelengths were observed from five selected intermixed regions on a single chip. These lasers showed no significant change in transparency current, internal quantum efficiency or internal propagation loss, which indicates that the material quality was not degraded after intermixing     

Observation of multiple resonance frequencies in stripe geometryInGaAs/InGaAsP/InP quantum-well lasers

Intensity fluctuation noise in strained InGaAsP/InP multi-quantum-well lasers is analyzed for both ridge-guided and broad-area gain-guided structures. A single resonance peak is observed in the noise spectrum for the ridge-guided laser, as expected. However, the noise spectrum for the broad-area lasers shows multiple (~2-5) resonance peaks, distinctly spaced, from ~2 to ~5 GHz. Combined with near-field measurements, the experiments show that these peaks originate from lasing filaments having significantly nonuniform optical power. The authors also determined the resonance frequency of the single-mode laser from both small-signal modulation and turn-on relaxation oscillation measurements and found the results to be consistent with the measured peak noise frequency     

Mode characteristics of large-optical-cavity V-channeled substrate inner stripe injection lasers

The dependence of mode characteristics on built-in refractive-index difference is studied for V-channeled substrate inner stripe lasers by the introduction of large-optical-cavity structure. Temperature dependence of the far-field pattern indicates that the waveguiding mechanism in these devices can be clearly classified into index guiding and gain guiding. At high light outputs, index-guided devices oscillate on a single longitudinal mode and gain-guided devices oscillate on multimodes. In the index-guided lasers, however, the mode stabilization occurs at higher light outputs in the lasers with smaller built-in refractive-index difference.     

Threshold current density reduction of strained AlInGaAs quantum-well laser

In the last decades, researchers have tried to implement novel optoelectronic devices with new semiconductor material compounds. There are few competitors in the race for more reliable, more efficient, pump sources for solid-state lasers. These diodes should operate at high power, intense brightness, and with low threshold current. The strained AlInGaAs-GaAs quantum-well (QW) laser is a promising candidate. In this study we optimized the growth parameters of strained AlInGaAs quantum wells using a model for linewidth broadening of photoluminescence, which was extended for the first time to handle quaternary alloys. This model enables us to identify the dominant contributions to the broadening. As a result of our growth parameters optimization technique, low threshold current density of simple broad-area lasers has been obtained, indicating a superior material quality. Moreover, we have studied for the first time the effect of indium and aluminum content and QW width on the threshold current density of quaternary AlInGaAs QW lasers. As a result of these studies the lowest known threshold current density for AlInGaAs on GaAs single QW broad-area laser has been achieved.     

Temperature dependence of threshold current for a quantum-well heterostructure laser

The threshold current density, J_th, of a quantum-well laser diode is calculated taking into account the quasi-two-dimensional nature of the heterostructure. The calculated value of J_th(T) for a quantum-well laser diode is found, in agreement with experiment, to be less temperature sensitive than that of a conventional double heterojunction laser. The step-like densities of states and the perturbed (hot) carrier distribution of a quasi-two-dimensional structure are responsible for the weaker temperature dependence. Supporting data on quantum-well Al_xGa_1-xAsGaAs heterostructure laser diodes grown by MO-CVD are presented showing that in the conventional expression J_th(T) = J_th(0) exp (T/T₀), T₀ can be as high as ～ 437°C.     

电流阻挡层结构对垂直发光二极管芯片老化特性之研究

发现ICP damage制作电流阻挡层的制程会导致垂直结构LED在老化过程中发生漏电。通过更换反射层的金属及EMMI&SEM分析,发现老化漏电的原因来源于反射金属——Ag的电迁移,迁移通道可能来源于ICP打开穿透位错的封口。在缺陷位错内填入低电迁移率金属并检测。结果表明,填入低电迁移率金属后既解决了老化漏电问题,同时不影响芯片的初始光电特性。     

Twin-transverse-junction stripe laser with linear light/current characteristic and low threshold

Lateral confinement of both light and carriers in the active region is achieved by creating twin transverse junctions with a deep Zn diffusion. The source is a stripe of SiO2 from which the Zn is diffused at low concentration into a highly n-doped double-heterostructure wafer. Threshold currents of around 30?40 mA have been measured and near and far fields of typically 3 ?m and 10°, respectively, have been observed (both to half intensity). The optical control achieved results in linear light/current characteristics and zero-order-mode operation.     

Theoretical and experimental analysis of leakage current in InGaAsPBH lasers with p-n-p-n current blocking layers

The dependence of the leakage current in 1.3-μm InGaAsP buried heterostructure (BH) lasers with p-n-p-n current blocking layers on well number, mesa width, and carrier density has been analyzed using a two-dimensional device simulator and compared with the electroluminescence (EL) emitted from InP layers. The analysis of the minority carrier flow reveals that the electron current flowing through the p-n-p-n current blocking layers is the dominant component of the leakage current. The measured EL intensity has two peaks at both sides of the n-blocking layer apart from the active layer. The EL intensity decreases with increasing well number and carrier density of the p-blocking layer, and increases with increasing mesa width. These results are consistent with the simulations     

InGaN-GaN MQW LEDs with current blocking layer formed by selective activation

Selective activation technique was used to define a semi-insulating current-blocking layer underneath the p-pad of InGaN-GaN multiple-quantum-well light-emitting diodes (LEDs). The output power of the LEDs at 20 mA was increased 10% because less current was injected underneath the opaque p-pad.     

A constantly sampled current controller with switch status dependent inner bound

In this paper, a constantly sampled current-controlled pulsewidth-modulation (PWM) strategy is proposed such that the controlled current can follow the command within a specified error bound to guarantee the desired good power quality. According to different previous switch statuses, a different inner bound is proposed for current error comparison to add the zero-mode control at the proper time to further reduce the switching frequency. Moreover, an analytic expression of the upper bound of the constant sampling period for the current controller to guarantee the desired performance is derived and some design criteria are given for proper coordination among the circuit parameters. Finally, some simulation and experimental results are given to demonstrate the validity of the proposed current-controlled PWM scheme.     

Integrated optical devices of InGaAsP/InP heterojunction phototransistor and inner stripe light-emitting diode

New integrated optical devices combining an InGaAsP/InP HPT and an inner-stripe LED are proposed and their fabrication processes are described. The device functions of light amplification, optical bistability, and optical switching are demonstrated in the 1-µm wavelength region.     

不同几何结构电光偏转器比较研究

为了发展性能优良的电光偏转器,采用傍轴近似分析了级联棱镜电光偏转器的折射率梯度等效表达式,总结出了不同几何结构电光偏转器的偏转角和偏转轨迹公式,在此基础上比较研究了4种不同几何结构电光偏转器的偏转特性和偏转轨迹,比较分析了梯形、喇叭形和抛物线形几何结构电光偏转器的偏转灵敏度,为较大角度电光偏转系统的设计提供了有意义的参考。     

Integrated optical devices of InGaAsP/InP heterojunction phototransistor and inner stripe light-emitting diode

New integrated optical devices combining an InGaAsP/InP HPT and an inner-stripe LED are proposed and their fabrication processes are described. The device functions of light amplification, optical bistability, and optical switching are demonstrated in the 1-μm wavelength region.     

Improved current efficiency in organic light-emitting devices with a hole blocking layer

A hole-blocking layer (HBL) of 4,7-diphenyl-1,10-phenanthroline (BPhen) is incorporated between the emitting layer (EML) and the electron transport layer (ETL) for a tris-(8-hydroxyqunoline)aluminum based organic light-emitting device (OLED). Such a structure helps to reduce the hole-leakage to the cathode, resulting in an improved current effi-ciency. The BPhen improves the balance of hole and electron injections. The current efficiency is improved compared with that of the device without the blocking layer. The highest luminous efficiency of the device with 6 nm BPhen acting as a blocking layer is 3.44 cd/A at 8 V, which is improved by nearly 1.5 times as compared with that of the de-vice without it.     

Novel transition between different configurations of planartransmission lines

New designs of coplanar waveguide (CPW)-microstrip, CPW-stripline, conductor backed CPW (CBCPW)-microstrip, and CBCPW-stripline transitions are presented. Simulation using the high frequency structures simulator (HFSS) shows that the return loss of the CPW-microstrip transition is less than -25 dB up to 11 GHz. Similarly is the CPW-stripline transition. In the case of two back to back CBCPW-stripline transitions, the return loss is less than -22 dB up to 9 GHz. Experimentally, the S ₁₁ of two back to back CBCPW-microstrip transitions on an alumina substrate is less than -15 dB up to 25 GHz     

The role of carrier transport on the current injection efficiency of InGaAsN quantum-well lasers

A theoretical and experimental study demonstrates that the current injection efficiency of InGaAsN quantum-well (QW) lasers can be significantly affected by carrier transport in the separate confinement heterostructure (SCH) region. An offset QW design is utilized to show the impact of hole transport on the temperature dependence of the external differential quantum efficiency and above threshold injection efficiency. A reduction of the current injection efficiency is found for structures which have significant hole transport times in the SCH.