High-speed, low-threshold InGaAsP semi-insulating buried crescentlasers with 22 GHz bandwidth

The authors have fabricated high-speed, low-threshold 1.3 μm InGaAsP semi-insulating buried crescent lasers with a CW 3 dB modulation bandwidth of 22 GHz and a threshold current as low as 6.5 mA at room temperature. This is the highest 3 dB modulation bandwidth ever reported for the planar-type semiconductor laser. These results were achieved by implementing a submicron photolithographic process in the channel etching to reduce the cavity width and a polyimide dielectric layer under the bonding pad area to minimize the electrical parasitics     

High-speed Schottky photodiode on semi-insulating GaAs

A high-speed GaAs photodiode has been fabricated on a GaAs semi-insulating substrate. The photodiode has an active area of 8 ?m × 15 ?m and a bandwidth in excess of 9 GHz. This Schottky photodiodes is suitable for monolithic integration with other optoelectronic components.     

Integratable, high speed buried ridge DFB lasers fabricated on semi-insulating substrates

The fabrication of buried ridge DFB lasers on semi-insulating substrates is described. A novel contacting mechanism was employed to give a series resistance of less than 4 Omega . Devices were fabricated at both 1.3 and 1.53 mu m with lasing thresholds as low as 16 mA. Single longitudinal mode operation was achieved with SMSR greater than 30 dB at both wavelengths. The structure gives an inherently low capacitance, which together with low threshold currents, low series resistance and fabrication on SI substrates makes these devices suitable for integration and high speed applications.<>     

High-speed electroabsorption modulators buried with ruthenium-doped SI-InP

InGaAlAs-InAlAs electroabsorption modulators are successfully fabricated using ruthenium (Ru)-doped semi-insulating (SI)-InP burying technology. A comparison of measured and calculated microwave characteristics reveals that there is no additional microwave loss because zinc diffusion is inhibited by the use of Ru-doped SI-InP layers. A small-signal electrooptical response with a -3-dB electrical bandwidth of over 50 GHz is demonstrated.     

Photoreflectance study of electric field distributions in semiconductors heterostructures grown on semi-insulating substrates

We have studied the photoref lectance (PR) spectra from a MBE grown heterostructure consisting of 200 nm of Ga_0.83Al_0.17As, a 800 nm GaAs buffer layer on a semi-insulating (100) LEC GaAs substrate. By varying both the pump beam wavelength and modulation frequency (up to 100 kHz) we are able to identify the component layers, their quality and the properties of the various interfaces. In this study we find evidence for a low density of interface states between the GaAs buffer layer and GaAlAs layer and a relatively large density of interface states between the substrate and buffer regions. These states, previously observed by Deep Level Transient Spectroscopy of doped structures, are presumably associated with the interface produced by MBE growth on etched and air exposed substrates. However, in our material, since the substrate is semi-insulating and the buffer layer is undoped, it is difficult to resolve these states spatially by C-V techniques. Our results show that the PR technique can be used to characterize low conductivity or semi-insulating structures such as enhancement mode MESFET and HEMT type devices and it may be useful for the in-situ characterization of epigrown surfaces and interfaces     

High-speed spiral-scan echo planar NMR imaging-I

An improved echo planar high-speed imaging technique using spiral scan is presented and experimental advantages are discussed. This proposed spiral-scan echo planar imaging (SEPI) technique employs two linearly increasing sinusoidal gradient fields, which results in a spiral trajectory in the spatial frequency domain (k-domain) that covers the entire frequency domain uniformly. The advantages of the method are: 1) circularly symmetric T2 weighting, resulting in a circularly symmetric point spread function in the image domain; 2) elimination of discontinuities in gradient waveforms which in turn will reduce initial transient as well as steady-state distortions; and 3) effective rapid spiral-scan from dc to high frequency in a continuous fashion, which ensures multiple pulsing with interlacing for further resolution improvement without T2 decay image degradation. Some preliminary experimental results will be presented and further possible improvements suggested.     

1.5 ?m region InP/GaInAsP buried heterostructure lasers on semi-insulating substrates

InP/GaInAsP buried heterostructure (BH) lasers for the 1.5 ?m region have been fabricated on semi-insulating InP substrates. The threshold current of the lasers is as low as 38 mA under CW operation at 25°C, which is nearly the same as for BH lasers fabricated on n-type InP substrates.     

Low pressure MOCVD growth of buried heterostructure laser wafers using high quality semi-insulating InP

Semi-insulating Fe doped InP has been grown by low pressure MOCVD at 100 mbar and 630° C. Complete activation of Fe below the solubility limit of 5 × 10₁₆ cm^-3 has been achieved by reducing the PH₃ concentration during crystal growth to the lowest value required to maintain good surface morphology of the layer. Diffusion of the Fe dopant and dopant spikes at the interface between the substrate and grown layer can be minimized by ensuring that the total Fe concentration in the layer does not exceed the diffusion threshold of 2 × 10¹⁷ cm⁻³. Growth of Fe doped InP around a double heterostructure mesa formed by reactive ion etching produces a structure without either growth of InP on the mesa or notches at the mesa sidewalls, even with minimal overhang of the dielectric mask. Examination of regrown heterostructures shows no evidence of interdiffusion of Fe and Zn, indicating that Fe diffusion has been successfully prevented. Completed lasers have threshold current densities of 2.5 kA/cm² at 20° C and initial aging results which indicate that these devices have good lasing characteristics and potentially high reliability.     

High-speed GaInAsP/InP buried-heterostructure optical intensity modulator with semi-insulating InP burying layers

GaInAsP/InP buried-heterostructure (BH) optical intensity modulators have been fabricated by the use of Fe-doped semi-insulating InP burying layers. The reduction of a parasitic capacitance due to the semi-insulating burying layers realised a wide modulation bandwidth of 11.2GHz. At a wavelength of 1.53/?m, an attenuation ratio of 20 dB at 26°C was achieved with an applied voltage of ?8.5 V.     

High-speed BiCMOS technology with a buried twin well structure

A buried twin well and polysilicon emitter structure is developed for high-speed BiCMOS VLSI's. A bipolar transistor of high cutoff frequency (fT= 4 GHz) and small size (500 µm²) has been fabricated on the same chip with a standard 2-µm CMOS, without degrading the device characteristics of the MOSFET. Latchup immunity is improved due to the low well resistance of the buried layer. The well triggering current is a 0.5-1.0 order of magnitude higher than that of a standard n-well CMOS. To evaluate the utility of this technology, a 15-stage ring oscillator of the 2NAND BiCMOS gate is fabricated. The gate has a 0.71-ns propagation delay time and 0.25-mW power dissipation at 0.85-pF loading capacitance and 4-MHz operation. Drive ability is 0.24 ns/pF, which is 2.5 times larger than that of the equal-area CMOS gate.     

Reliability and degradation behaviors of semi-insulating Fe-dopedInP buried heterostructure lasers fabricated by RIE and MOVPE

We clarified the degradation behaviors of semi-insulating buried heterostructure lasers in which mesa structures were fabricated by reactive ion etching (RIE) and then buried in semi-insulating Fe-doped InP grown by metal organic vapor phase epitaxy (MOVPE). The degradation rate and mode correlated with the quality of the buried heterostructure (BH) interface. Based on the correlation, a condition for highly stable semi-insulating Fe-doped InP buried heterostructure (SIBH) lasers was demonstrated and confirmed experimentally and statistically     

Effects of a buried p-layer on alpha-particle immunity of MESFET's fabricated on semi-insulating GaAs substrates

Measurements of alpha-particle-induced charge are carried out for the first time on both conventional MESFET's fabricated directly on semi-insulating GaAs substrates and MESFET's with a buried p-layer. The maximum collected charge is found to be 65 fC in the MESFET's with a buried p-layer, one order smaller than in conventional MESFET's.     

High-speed electroabsorption modulator with strip-loaded GaInAsP planar waveguide

We describe fabrication and characterization of an electroabsorption (EA) light modulator (LM) with a strip-loaded GaInAsP planar waveguide. The EA LM's were fabricated from hydride vapor-phase-epitaxy (VPE) grown wafers. The electroabsorption, the insertion loss, the electrical properties, and the modulation characteristics were investigated for the EA LM's. The drive voltage at a 99-percent modulation depth has been noticeably reduced to 4.5 V by optimizing the thicknesses of the epitaxial layers. The total capacitance of 1.5 pF was obtained by inserting an insulating film under the wire-bonding pad and by improving the mount design. Consequently, a 3-dB bandwidth of 3.8 GHz has been achieved and a pulse modulation operation under 2 Gbit/s nonreturn-to-zero (NRZ) pseudorandom pattern has also been confirmed. Moreover, the dynamic spectra of the EA modulators were measured for the first time. A spectral broadening factor α has been determined to be 1-4 from a relative strength of the sideband to the carrier and it has been experimentally found to decrease with increasing the electric field inside the absorptive waveguide. As the other measures of merit for the EA LM's, the extinction ratio over 23 dB and the insertion loss of 10-14 dB including a coupling loss due to an end-fire method were obtained. As a whole, these results have exhibited that the EA LM is a promising external modulator which will be monolithically integrated into a gigabit per second optical source with a dynamic single-mode laser.     

Complex natural resonances of conducting planar objects buried in adielectric half-space

A scheme is presented to incorporate a mixed potential integral equation (MPIE) using Michalski's “formulation C” with the method of moments (MoM) for analyzing the scattering of a plane wave from conducting planar objects buried in a dielectric half-space. The robust complex image method with a two-level approximation is used for the calculation of the Green's functions for the half-space. To further speed up the computation, an interpolation technique for filling the matrix is employed. While the induced current distributions on the object's surface are obtained in the frequency domain, the corresponding time domain responses are calculated via the inverse fast Fourier transform (FFT). The complex natural resonances of targets are then extracted from the late time response using the generalized pencil-of-function (GPOF) method. The authors investigate the pole trajectories as they vary the distance between strips and the depth and orientation of single, buried strips. The variation from the pole position of a single strip in a homogeneous dielectric medium was only a few percent for most of these parameter variations     

Fe-doped InP semi-insulating buried heterostructure for high speed and high power operations in directly modulated semiconductor laser

A buried heterostructure based on Fe-doped InP semi-insulating layers is optimised for both high output power and large modulation bandwidth operations up to 70/spl deg/C in a 10 Gbit/s directly modulated 1.3 /spl mu/m InGaAsP/InP distributed feedback laser. The slope efficiency of 0.19 W/A and -3 dB bandwidth of 10 GHz at 1.5 times threshold current is demonstrated experimentally.     

InGaAs/GaAs 0.98 μm semi-insulating blocked planar buriedheterostructure lasers employing InGaAsP cladding layers

MOVPE-grown InGaAs/GaAs strained-layered lasers emitting at 0.98 μm have been fabricated using InGaAsP as an alternative to AlGaAs in the cladding layers. Semi-insulating blocked planar buried heterostructure lasers 2.5 μm wide have thresholds as low as 8 mA for 350 μm long devices. With the addition of reflective coatings, slope efficiencies of 0.67 mW/mA and output powers of 60 mW at 160 mA have been obtained     

High-speed low-power DCFL using planar two-dimensional electron gas FET technology

Planar two-dimensional electron gas FETs (TEGFETs) have been shown to have ultra-high speed and low power in DCFL circuits operating at room temperature: 18.4 ps at 900 ?W and 32.5 ps at 62 ?W. The latter result and the simplicity of the process involved are compatible with VLSI requirements.     

Entirely aluminum free 905-nm wavelength buried heterostructurelaser by reactive ion etching and semi-insulating GaInP:Fe regrowth

Selective regrowth of semi-insulating Ga_0.51In_0.49 P: Fe (resistivity ≈1×10¹² Ω cm) has been realized for the first time to fabricate entirely Al free buried heterostructure GaInP/GaInAsP/GaAs laser emitting at 905 mn. The fabrication procedure and the laser characteristics are presented,     

1.55 μm InGaAsP/InP laser buried in a high-resistivity epitaxiallayer on a semi-insulating InP substrate

A buried heterostructure (BH) 1.55 μm laser embedded in a high resistivity epitaxial layer on a semi-insulating substrate is described. This device has a planar surface and both a p- and an n-type electrode on the same side, facilitating integration of electronic devices. Its threshold current is typically 9 mA. Its small signal 3 dB modulation bandwidth was 14 GHz due to the reduction of device resistance and capacitance. No degradation was observed in an aging test at 50°C even after more than 3000 h     

Reliability and degradation behaviors of semi-insulating Fe-doped InP buried heterostructure lasers fabricated by movpe and dry etching technique

We clarified the degradation behavior of semi-insulating buried heterostructure lasers in which mesa structures were fabricated by RIE and then buried by MOVPE. The degradation rate and mode correlated with the quality of the BH interface. Based on the correlation, a condition for highly stable SIBH lasers was demonstrated and confirmed experimentally and statistically.