P.D. Dapkus

Dense arrays of ordered GaAs nanostructures by selective area growth on substrates patterned by block copolymer lithography

GaAs has been selectively grown in a hexagonally ordered array of nanometer-scale holes with a density as high as ∼1011/cm2 by metalorganic chemical vapor deposition. This array of holes was created using block copolymer lithography, in which a thin layer of diblock copolymer was used as an etching mask to make dense holes in a 15-nm-thick SiNx film. These selectively grown nanoscale features are estimated to be 23 nm in diameter with narrow lateral size and height distributions as characterized by field-emission scanning electron microscopy and tapping mode atomic force microscopy. The narrow size distribution and uniform spatial position of the nanoscale dots we report offer potential advantages over self-assembled dots grown by the Stranski–Krastanow mode.

Ultralow threshold current vertical-cavity surface-emitting lasers with AlAs oxide-GaAs distributed Bragg reflectors

An electrically-pumped, vertical-cavity, surface-emitting laser (VCSEL) using an AlAs oxide-GaAs DBR above the AlGaAs-GaAs-InGaAs gain region and a conventional AlAs-GaAs DBR below is described. By selective oxidation, devices with current flow apertures of different areas are fabricated, and in 8-/spl mu/m-square devices, threshold currents as low as 0.22 mA are achieved. Being the first electrically-pumped VCSEL to utilize the oxide-based DBR, it demonstrates that the oxide-based DBR is of sufficient quality to realize submilliampere threshold currents.<<ETX>>

Vertical resonant couplers with precise coupling efficiency control fabricated by wafer bonding

A fabrication technique to create complex three-dimensional waveguide devices is effected by using wafer bonding to process two sides of an epitaxial structure. Vertical resonant couplers with precise control over coupling efficiency are demonstrated.

Lithographic tuning of a two-dimensional photonic crystal laser array

One attraction of photonic crystals is the ability to control optical device characteristics by lithographically varying the geometry. In this letter, we demonstrate a 10/spl times/10 array of optically pumped two-dimensional (2-D) photonic crystal defect lasers with varying lattice parameters. By adjusting the photonic crystal interhole spacing as well as the hole diameter we are able to tune the laser wavelength from 1500 to 1625 nm on a monolithic InP-InGaAsP wafer. A wavelength resolution of 10 nm from device to device was obtainable, limited by the lithography and etching tolerances of our fabrication method.

GAN GROWTH ON SI(111) SUBSTRATE USING OXIDIZED ALAS AS AN INTERMEDIATE LAYER

We have demonstrated that GaN can be grown epitaxially by atmospheric pressure metalorganic chemical vapor deposition on an aluminum oxide compound layer utilized as an intermediate layer between GaN and a Si(111). X-ray diffraction measurement indicates that single-crystal hexagonal GaN with its basal plane parallel to the Si(111) plane is grown. Using a scanning electron microscope, the macroscopic evolution of GaN grown on the AlOx/Si(111) substrate is found to be similar to that of GaN grown on a sapphire(0001) substrate. Cathodoluminescence (CL) spectrum shows a unique emission that consists of several peaks with the intensity comparable to that of the near-band-edge emission. Unique characteristics in CL spectrum are discussed in terms of a possible oxygen contamination of GaN grown on the AlOx/Si(111) substrate.

Extended tuning range in sampled grating DBR lasers

The authors demonstrate, for the first time, successful implementation of a distributed Bragg reflector laser with two sampled grating mirrors, which they previously predicted should give tuning range in excess of 50 nm. This device uses a uniform grating pitch throughout the structure, and relies on the same fabrication technology as a standard DBR laser. Initial results show 57 nm of mathematical tuning at 1.475 mu m with side-mode suppression ratio (SMSR)>30 dB over much of the tuning range. The observed change in operating wavelength versus mirror currents along with below threshold spectra agree with theoretical expectations.<<ETX>>

Electrically-pumped vertical-cavity lasers with Al x O y -GaAs reflectors

We have fabricated the first electrically-pumped vertical-cavity surface-emitting lasers (VCSELs) which use oxide-based distributed Bragg reflectors (DBRs) on both sides of the gain region. They require a third the epitaxial growth time of VCSELs with semiconductor DBRs. We obtain threshold currents as low as 160 /spl mu/A in VCSELs with an active area of 8 /spl mu/m/spl times/8 /spl mu/m using a two quantum well InGaAs-GaAs active region. By etching away mirror pairs from the top reflector, quantum efficiencies as high as 61% are attained, while still maintaining a low threshold current of 290 /spl mu/A.

GaAs/AlGaAs quantum well lasers with active regions grown by atomic layer epitaxy

Atomic layer epitaxy (ALE) is a relatively new crystal growth technique which allows control of the growth process at the monolayer level through a self‐limiting, surface‐controlled growth mechanism. We report here the use of ALE to grow high‐quality GaAs/AlGaAs quantum wells and the first successful demonstration of an injection laser with a quantum well active region grown by ALE. Room‐temperature threshold current densities as low as 640 A/cm2 have been achieved in nonoptimized separate confinement structures.

Low-threshold-current-density 1.5 mu m lasers using compressively strained InGaAsP quantum wells

A low-threshold current density (J/sub th/) of 140 A/cm/sup 2/ for broad-area 1.5- mu m semiconductor lasers with uncoated facets is demonstrated at a cavity length of 3.5 mm. This was achieved by the use of a single InGaAsP quantum well (QW) of 1.8% compressive strain inside a step-graded InGaAsP waveguide region. Low-cavity losses of 3.5 cm/sup -1/ and a relatively wide quantum well as compared to InGaAs wells of equivalent strain contribute to this high performance. Double QW devices of 2 mm length showed threshold current densities of 241 A/cm/sup 2/. Quaternary single and double QWs of similar width but only 0. 9% strain gave slightly higher threshold current density values, but allowed growth of a 4 QW structure with a J/sub th/ of 324 A/cm/sup 2/ at L=1.5 mm.<<ETX>>

Vertically coupled InP microdisk switching devices with electroabsorptive active regions

InP vertically coupled microdisk resonator/waveguide switching devices with an electroabsorptive (EA) active region are demonstrated for the first time. The devices exhibit single-mode operation, large free spectral range of 10.5 nm and a high quality factor of 5700. The EA effect provides a way of loss-trimming the resonant characteristics. Active switches, routers, and fast modulators based on these devices are envisioned as part of a WDM system.