C.H. Lin

Semiconductor lasers on Si substrates using the technology of bonding by atomic rearrangement

We demonstrated InGaAs/GaAs strained quantum well lasers on silicon substrates. The epitaxial layers for lasers were first grown on a GaAs substrate and then bonded to a silicon substrate using the technology of bonding by atomic rearrangement. Covalently bonded III‐V/Si heterointerface was confirmed by the cross‐sectional transmission electron microscopy. The ridge waveguide lasers on Si substrates lasing at about 1 μm wavelength have a 12 mA threshold current and a 56% external quantum efficiency at room temperature, at pulsed condition. Both the threshold current and the external quantum efficiency are close to the values of lasers on GaAs substrates. The technology of bonding by atomic rearrangement will be useful for making optoelectronic integrated circuits on Si.

Overcoming the pseudomorphic critical thickness limit using compliant substrates

We demonstrated the high‐quality molecular beam epitaxy growth of exceedingly thick In0.14Ga0.86As pseudomorphic layers on thin, free‐standing, compliant GaAs substrates. We first fabricated 800‐A‐thick compliant platforms before growing a lattice‐mismatched layer on the platform. The layer we grew exceeds its usual critical thickness by about twenty times without strain relaxation. X‐ray analysis confirms a shift in the InGaAs peaks grown on the compliant substrate, indicating an unrelaxed strain of 0.9%. Moreover, atomic force microscope profiles verify that layers grown on compliant substrates are much smoother than layers grown on a plain substrate.

Dielectrically-bonded long wavelength vertical cavity laser on GaAs substrates using strain-compensated multiple quantum wells

We present a novel low temperature bonding technique for fabricating long wavelength vertical cavity surface emitting lasers (VCSELs). The technique relies on a 750 /spl Aring/-thick intermediate spin-on glass layer to join a highly efficient InP-based InGaAs-InGaAsP strain-compensated multiple quantum well (SC-MQW) gain medium on a GaAs substrate. We fabricated the device on GaAs in order to take advantage of highly reflective AlAs-GaAs Bragg reflectors. The optically-pumped device has a low threshold pump power of 4.2 kW/cm/sup 2/ at room temperature and operates at a wavelength of 1.44 /spl mu/m.<<ETX>>

Photopumped long wavelength vertical‐cavity surface‐emitting lasers using strain‐compensated multiple quantum wells

We report optically pumped long wavelength vertical‐cavity surface‐emitting lasers (VCSELs) made of strain‐compensated multiple quantum wells. The structure of the VCSELs consists of 30 pairs of compressive strained wells and tensile strained barriers as the gain medium and Si/SiO2 dielectric mirrors. The lasers operate at 1.59 μm wavelength. The threshold power density was measured to be 3 kW/cm2 at room temperature, corresponding to a threshold current density of about 2 kA/cm2. The VCSELs have a characteristic temperature T0 of 90 K between 10 and 60 °C, and 60 K from 70 to 110 °C.

Empirical formulas for design and optimization of 1.5 mu m InGaAs/InGaAsP strained-quantum-well lasers

The effects of strain and number of quantum wells on optical gain, differential gain, and nonlinear gain coefficient in 1.55- mu m InGaAs/InGaAsP strained-quantum-well lasers are theoretically investigated. Well-approximated empirical expressions are proposed to model these effects. Using these formulas, one can easily and accurately predict the performance of a laser diode for a given structure. Therefore, these empirical formulas are useful tools for design and optimization of strained quantum well lasers. As a general design guideline revealed from the empirical formulas, the threshold current is reduced with the compressive strain, and the modulation bandwidth is most efficiently increased with the number of wells.<<ETX>>

Cascade self-induced holography: a new grating fabrication technology for DFB/DBR lasers and WDM laser arrays

A method of fabricating submicron gratings for optoelectronic devices from a glass mask was proposed and demonstrated. The glass mask has gratings on both sides with a period of at least four times the final feature size. By introducing an offset to the grating periods on the mask, one can achieve multiple-period gratings with a very fine period spacing for advanced wavelength-division multiplexing (WDM) devices. In this paper, we demonstrated 0.5-/spl mu/m second-order gratings for 1.55-/spl mu/m DFB lasers and gratings with a 6-/spl Aring/ period difference for a four-channel WDM laser array using only optical sources. The Moire pattern caused by the spatial frequency beating was also observed and discussed. The Moire pattern could serve as an effective tool to measuring wavelength channel spacing between devices with an unprecedented (0.1 /spl Aring/) resolution.

New grating fabrication technology for optoelectronic devices: Cascaded self‐induced holography

A method of fabricating submicron gratings for optoelectronic devices from a glass mask was proposed and demonstrated. The glass mask has gratings on both sides with a period of at least four times of the final feature size. By modifying the grating periods on the mask, one can achieve multiple‐period gratings with a very fine period spacing for advanced wavelength division multiplexing (WDM) devices. In this letter, we demonstrated 0.5 μm second‐order gratings for 1.55 μm distributed‐feedback lasers and gratings with a 6 A period difference for WDM laser arrays using only optical sources.

ON NONUNIFORM PUMPING FOR MULTIPLE-QUANTUM WELL SEMICONDUCTOR LASERS

Optical gain distribution among quantum wells for (strained) multiple‐quantum well (MQW) lasers was analyzed to understand the effect of nonuniform pumping. The nonuniform gain distribution is mainly caused by stagnant hole transport across the quantum wells. Contrary to what people expected, neither uniformly p‐doped MQWs nor selectively p‐doped MQWs can alleviate the nonuniform pumping problem. The most effective solution is employing an exponential p‐doping profile which can counterbalance the nonuniform injection effect. Our simulation results showed that such an exponential p‐doping profile has a characteristic length around one‐half of the ambipolar diffusion length.

Long wavelength vertical cavity laser using strain-compensated multiple quantum wells on GaAs substrates

We present an optically pumped long wavelength vertical cavity surface emitting laser using an InGaAs/InGaAsP strain-compensated multiple quantum well gain medium fabricated an a GaAs substrate. The device relies on an 800 /spl Aring/-thick intermediate spin-on glass layer to join the high-gain InP-based gain medium with highly reflective GaAs-based AlAs/GaAs Bragg reflectors. At room temperature, the device operates at 1.44 /spl mu/m and has a low threshold pump power of 4.2 KW/cm/sup 2/.

New technology for fabricating multiple pitch gratings for WDM laser arrays

For high-capacity wavelength division multiplexing (WDM) optical communication systems, distributed feedback (DFB) laser arrays having a nanometer wavelength spacing are highly desirable. Most of the WDM laser arrays fabricated today used E-beam lithography to achieve accurate control of the channel spacing. However, E-beam lithography is not suitable for high volume production because of its low throughput and high cost. Recently, we developed a new fabricating process, cascaded self-induced holography, to form submicron gratings. This process is simple, reliable, and insensitive to vibrations and environmental changes. In this paper, we use cascaded self-induced holography to demonstrate multiple grating pitches having a period difference of a few angstroms between adjacent devices. This technique is particularly attractive for WDM laser arrays.