P.S.D. Lin

GROWTH OF HIGH QUALITY ALINAS BY LOW PRESSURE ORGANOMETALLIC CHEMICAL VAPOR DEPOSITION FOR HIGH SPEED AND OPTOELECTRONIC DEVICE APPLICATIONS

In this paper, we report on the low pressure organometallic chemical vapor deposition of AlInAs lattice matched to InP and the effect of the substrate temperature and V/III ratio on the layers grown. High quality AlInAs with X-ray and photoluminescence (5 K) linewidths of 21 arc sec and 15 meV, respectively, was obtained. It is demonstrated that a high growth temperature and a high arsine flow rate are necessary for obtaining good electrical and optical properties. A discrepancy was shown to exist between C-V and Hall derived carrier concentrations probably due to deep levels affecting the C-V measurements and a two-dimensional electron gas (2DEG) at the AlInAs/InP interface affecting the Hall measurements. The existence of a 2DEG at the AlInAs/InP interface, with a sheet density of 2.9×1011 cm-2 and a mobility of 11050 cm2/V°s at 4 K, was shown using Shubnikov-De Haas measurements. A correlation was made between oxygen or an oxygen related complex and high C-V measured carrier concentrations and large leakage currents in reverse biased Schottky contacts. An intense emission at ~1.2 eV, present in 5 K photoluminescence spectra of AlInAs/InP, was attributed to a spatially indirect transition across the AlInAs/InP interface. Conduction and valence band offsets of 448.8 and 324.3 meV, respectively, were deduced from the energy of this transition. Self aligned 0.25 μm gate high electron mobility AlInAs/GaInAs transistors with a transconductance as high as 1150 mS/mm and ft = 80 GHz at room temperature were fabricated. Finally, metal-semiconductor-metal photodetectors with a leakage current as low as 5 nA at 5 V, breakdown voltage greater than 25 V, responsivity of 0.42 A/W at 1.3 μm wavelength, and a bandwidth of 8 GHz were demonstrated.

Strain-induced lateral confinement of excitons in GaAs-AlGaAs quantum well microstructures

We report evidence for lateral confinement of excitons within a continuous two‐dimensional GaAs‐AlGaAs quantum well. The confinement to ‘‘wires’’ within the well was produced by partially etching a pattern through the upper AlGaAs barrier. We propose a new mechanism, that of patterned strain, for lateral quantum confinement of carriers in semiconductor microstructures, to explain our results.

Multiwavelength DFB laser arrays with integrated combiner and optical amplifier for WDM optical networks

In this paper, we describe the design, fabrication and performance of multiwavelength DFB laser arrays with integrated combiner and optical amplifier built for wavelength-division-multiplexed (WDM) optical networks. The goal is to reduce the per-wavelength transmitter cost in both initial procurement and subsequent operation. Using photonic integration, we have addressed and resolved several important issues related to laser arrays such as wavelength accuracy, output power, high-speed modulation and optical packaging. State of the art results have been obtained. By the use of wavelength redundancy and proximity effect, wavelength deviations of /spl plusmn/0.2 nm or less from the designated eight-wavelength comb have been achieved with high yield. Simultaneous operation of ten wavelengths has also been demonstrated. In spite of the inherent splitting loss of 13 dB, high-output powers of about -13 and 0.5 dBm per wavelength have been measured, under simultaneous operation, into a single-mode fiber (SMF) without and with on-chip optical amplification, respectively. The DFB laser has a 3-dB bandwidth of 9 GHz. A 2.5-Gb/s (OC-48) error-free transmission through 120 km conventional SMF has been demonstrated under single channel operation. The electrical crosstalk from neighboring channels cause negligible degradation to the eye diagram and the bit-error-rate (BER) curve at a bit rate of 2.5 Gb/s. The optical crosstalk due to four-wave mixing and cross-gain modulation (XGM) of the semiconductor optical amplifier (SOA) is also characterized. The impact of this integrated laser array on WDM optical networks is assessed in the conclusion.

Multiwavelength DFB laser array transmitters for ONTC reconfigurable optical network testbed

We discuss the design, fabrication, and performance of experimental multiwavelength laser array transmitters that have been used in the reconfigurable optical network testbed for the Optical Network Technology Consortium (ONTC). The experimental four-node multiwavelength network testbed is SONET/ATM compatible. It has employed multiwavelength DFB laser arrays with 4 nm wavelength spacing for the first time. The testbed has demonstrated that multiwavelength DFB laser arrays are indeed practical and reproducible. For the DFB laser arrays used in such a network the precise wavelength spacing in the array and the absolute wavelength control are the most challenging tasks. We have obtained wavelength accuracy better than /spl plusmn/0.35 nm for all lasers, with some registered to better than /spl plusmn/0.2 nm. We have also studied the array yield of our devices and used wavelength redundancy to improve the array yield. Coupling efficiencies between -2.1 to -4.5 dB for each wavelength channel have been obtained. It is achieved by using specially designed lensed fiber arrays placed on a silicon V-grooved substrate to exactly match the laser spacing. The transmitter consisted of a multichip module containing a DFB laser array, an eight-channel driver array based on GaAs ICs, and associated RF circuitry.

Strain‐induced confinement of carriers to quantum wires and dots within an InGaAs‐InP quantum well

We describe a novel method of confining carriers by deliberately creating large inhomogeneous strain patterns in a quantum well. The strain modulates the band gap to provide lateral quantum confinement for excitons. Here, we generate strain confinement in an InGaAs quantum well by reactive ion beam assisted etching through an overlying compressed pseudomorphic quaternary layer using etch masks patterned by electron beam lithography. Photoluminescence spectra of arrays of wires and dots show red‐shifted band gaps in direct evidence of lateral confinement. We compare our results to finite element calculations of the inhomogeneous strain in an InP substrate from a compressed overlayer patterned into rectangular wires.

High‐speed electrical sampling by fs photoemission

We propose and demonstrate a new method for contactless sampling of high‐speed electrical signals, by spectral analysis of photoelectrons emitted when a signal‐carrying conductor is illuminated by ultrashort light pulses. We present time‐resolved measurements of sub‐ns electrical signals on a gold transmission line on GaAs using three‐photon photoemission induced by 80 fs visible laser pulses, and we discuss the temporal resolution of these measurements. This method is applicable to devices and circuits on any semiconductor.

A novel technique for the preservation of gratings in InP and InGAAsP and for the simultaneous preservation of InP, InGaAs, and InGaAsP in OMCVD

Regrowth steps in the fabrication of optoelectronic devices often require simultaneous preservation of InP, InGaAs, and InGaAsP during the initial heat-up before growth. In addition, if a grating is present on the wafer surface, it is necessary to prevent mass transport from eliminating it. We report on the use of As4 and P4 vapors to preserve gratings in InP and InGaAsP and also simultaneously preserve InP, InGaAs, and InGaAsP. Thermodynamic calculations are used to show that at 625°C InP and InGaAs are stable in As4 and P4 but not in AsH3 and PH3, respectively. The preservation technique developed in this study was used to fabricate high performance multiple quantum well planar buried heterostructure lasers and travelling wave amplifiers.

Optical properties of quantum wires produced by strain patterning of GaAsAlGaAs quantum wells

Abstract We have confined excitons to wires within continuous GaAsAlGaAs quantum wells. The confinement is produced by inhomogeneous strain created by patterning and etching a compressively stressed overlayer of amorphous carbon. Potential wells for excitons beneath 400 nm wide wires are 31 meV, as measured by the red-shift of the exciton emission. We compare our results to expectations based upon finite-element calculations of the strain tensor, and discuss the complicated effect of the inhomogeneous strain on valence-band structure.

Picosecond temporal resolution photoemissive sampling

Sampling measurements of electrical transients generated photoconductively on a 5‐μm gold coplanar transmission line on GaAs were performed via multiphoton photoemission. A temporal resolution of 5 ps was achieved, with a voltage sensitivity of 10 mV/(Hz)1/2. These results confirm that the temporal resolution attainable by this technique is enhanced when the dimensions of the structure under examination are reduced.

Excitation spectroscopy of strain-patterned semiconductor wires

Abstract We show here the first excitation spectroscopy of semiconductor wires produced by strain patterning. We observe efficient trapping of laterally diffusing excitons into the wires. In addition, we report a strong anisotropy in the optical selection rules that results from the mixing of the light and heavy hole by the anisotropic strain.