J. Lopata

High-power laser light source for near-field optics and its application to high-density optical data storage

A laser light source for high-resolution near-field optics applications with an output power exceeding 1 mW (104 times the power from previous sources) and small (300 nm square to less than 50 nm square) output beam size is demonstrated. The very-small-aperture laser (VSAL) tremendously expands the range of applications possible with near-field optics and increases the signal-to-noise ratios and data rates obtained in existing applications. As an example, 250-nm-diam marks corresponding to 7.5 Gb/in.2 storage density have been recorded and read back in reflection and transmission on a rewritable phase-change disk at 24 Mb/s with a 250-nm-square aperture VSAL. VSALs potentially enable data storage densities of over 500 Gb/in.2 (up to 100 times today’s magnetic or optical storage densities).

Coherent terahertz radiation detection: Direct comparison between free-space electro-optic sampling and antenna detection

We compare the use of free-space electro-optic sampling (FSEOS) with photoconducting antennas to detect terahertz (THz) radiation in the range of 0.1–3 THz. For the same average THz power and low-frequency modulation, signal-to-noise ratio and sensitivity are better with antenna detection at frequencies smaller than 3 THz. When the modulation frequency is increased to more than 1 MHz in FSEOS, both detection schemes have comparable performance. Using a singular-electric-field THz emitter, we demonstrate the feasibility of a THz imaging system using real-time delay scanning in FSEOS and only 20 mW of laser power.

Design and performance of singular electric field terahertz photoconducting antennas

We present new designs of more efficient terahertz (THz) radiation emitters and detectors enhanced by electric field singularities using sharp and laterally offset electrodes. We compare the performances of the terahertz emission and different polarization properties resulting from these structures. An average THz radiation power of 3 μW is achieved under 20 mW excitation, calibrated by free space electro-optic sampling. We also study the gap size dependence of the THz radiation, and find an absence of a positive electrode effect in the small gap limit.

Vertical-cavity surface-emitting lasers flip-chip bonded to gigabit-per-second CMOS circuits

We describe the first integration of vertical-cavity surface-emitting laser arrays with gigabit-per-second CMOS circuits via flip-chip bonding.

Passivation of Si donors and DX centers in AlGaAs by hydrogen plasma exposure

The effect of hydrogen plasma exposure upon shallow donors and DX centers in silicon‐doped AlGaAs has been investigated by deep level transient spectroscopy and capacitance versus voltage measurements. Following exposure to a hydrogen plasma for 30 min at 250 °C, the shallow level and DX center activity are reduced by an order of magnitude throughout a 1.6‐μm‐thick layer of molecular beam epitaxially grown AlGaAs. Isochronal annealing studies showed that both the shallow donor and DX center electrical activity recover together at about 400 °C. The shallow donor recovery mimics the behavior of donors in GaAs and has an activation energy of 2.0 eV. The DX center recovery shows a distribution of activation energies centered at 2.1 eV with a full width at half‐maximum of 0.25 eV. The hydrogen passivation chemistry of DX centers and shallow donors support models in which isolated Si impurities give rise to both DX behavior and shallow levels.

Hydrogen passivation of acceptors in p‐InP

The problem of hydrogenation of InP without surface degradation has been surmounted by exposure of the InP surface to a hydrogen plasma through a thin SiNx(H) cap layer. This layer is H permeable at the hydrogenation temperature of 250 °C, but P or PH3 impermeable thus minimizing PH3 loss and the attendant In droplet formation. In contrast to our results for this type of plasma exposure of GaAs, we find that shallow acceptors in InP are heavily passivated, whereas shallow donors are only very weakly affected. For example, p+‐InP(Zn) of 3×1018 cm−3 has its residual hole concentration reduced to ≤3×1014 cm−3 over a depth of 1.3 μm by a 250 °C, 0.5 h deuteration. The presence of acceptors impedes H (or D) indiffusion, as indicated by D diffusion under the same conditions occurring to depths of 18 and 35 μm in p‐InP (Zn, 2×1016 cm−3) and n‐InP (S or Sn), respectively. Annealing for 1 min at 350 °C causes the acceptor passivation to be lost and the hole concentration to be returned to its prehydrogenation leve...

Vibrational characteristics of acceptor‐hydrogen complexes in silicon

Acceptor‐hydrogen complexes for the group III acceptors, B, Al, and Ga, in Si have been studied with low‐temperature infrared spectroscopy. The Si‐H stretching band narrows dramatically upon cooling to low temperature thereby aiding the detection of the vibrations of the Al and Ga acceptor‐H complexes. The frequency 2201 cm−1 we have measured for the Al‐H complex is in reasonable agreement with the prediction made by G. G. DeLeo and W. B. Fowler [Phys. Rev. B 31, 6861 (1985)] (2220 cm−1 for a 〈111〉 interstitial configuration for the H). Assignment of the new vibrational bands is confirmed by isotopic substitution. The strength of the absorption provides evidence that the passivation is not the result of compensation alone and that a major fraction of the passivated acceptors result in acceptor‐H complexes. A new, low‐energy excitation of the acceptor‐hydrogen complexes gives rise to a sideband to the main stretching vibration and explains the pronounced energy shift and narrowing of the spectra upon cooli...

HYDROGEN IN CARBON-DOPED GAAS GROWN BY METALORGANIC MOLECULAR BEAM EPITAXY

Atomic profiles show that hydrogen is incorporated in GaAs:C that has been grown by metalorganic molecular beam epitaxy. The hydrogen concentration has been found to be about 5% of the carbon concentration for our growth conditions. An infrared absorption study shows that this hydrogen is involved in stable C‐H complexes. At the lower C concentrations (<1019 cm−3) the CAs‐H complex is the dominant species involving C and H. At higher C concentrations new complexes involving C and H appear.

16 x 16 VCSEL array flip-chip bonded to CMOS VLSI circuit

We report the flip-chip bonding of a 16/spl times/16 array of 970-nm vertical-cavity surface-emitting lasers (VCSELs) to an array of silicon CMOS driver circuits. The small-signal bandwidth of a flip-chip bonded VCSEL is in excess of 4 GHz. Individual VCSELs are capable of being modulated by the CMOS circuits at 1 Gb/s. The thermal impedance of the flip-chip bonded VCSELs is 1/spl deg/C/mW. The measured crosstalk suppression between channels is approximately 20 dB. Simultaneous parallel testing of up to 80 VCSELs at 1 Gb/s per VCSEL is demonstrated.

Growth and characterization of high yield, reliable, high-power, high-speed, InP/InGaAsP capped mesa buried heterostructure distributed feedback (CMBH-DFB) lasers

The capped-mesa buried-heterostructure distributed-feedback (CMBH-DFB) laser structure requires three epitaxial growths and is designed to allow good control of the width of the active layer using straightforward chemical etching techniques. The base structure, which contains the active layer, was fabricated using a variety of epitaxial techniques: liquid-phase epitaxy, hydride vapor-phase epitaxy (VPE) and metalorganic vapor-phase epitaxy (MOVPE). The final cap growth was done using hydride VPE. High yields of low-threshold high-power DFB lasers were produced from a number of wafers at emission wavelengths of 1.3 and 1.55 mu m. >