C.L. Chua

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.

High‐performance InGaAs photodetectors on Si and GaAs substrates

In this work, we demonstrate record low dark current operation of InGaAs (1.55 μm) p‐i‐n photodetectors on both silicon and gallium arsenide substrates using a wafer bonding technique. The photodetectors were made by first bonding the p‐i‐n epitaxial layers to the Si and GaAs substrate followed by chemical removal of the host (InP) substrate from the p‐i‐n structure. The photodetector was then fabricated atop the newly exposed p‐i‐n epilayers. Dark currents of as low as 57 pA on a GaAs substrate and 0.29 nA on a Si substrate were measured under 5 V reverse bias. The responsivity at 1.55 μm wavelength was measured to be 1 A/W, corresponding to an external quantum efficiency of 80%. The series resistance measured across the bonded interface gave 17 Ω on GaAs and 350 Ω on Si, respectively.

Low-threshold 1.57-μm VC-SEL's using strain-compensated quantum wells and oxide/metal backmirror

We present an electrically-pumped long wavelength vertical cavity surface-emitting laser (VC-SEL) using strain-compensated multiple quantum well gain medium and an oxide/metal backmirror. Design flexibilities such as using oxide/metal mirrors are possible because of the exceedingly high optical gain provided by strain-compensated multiple quantum wells. The gain medium is bonded to various substrates, including InP and Si, prior to device processing. This substrate transfer process facilitates heat sinking, and can be useful in the integration of VC-SELs with other devices. The device operates at a single wavelength of 1.57 /spl mu/m, and has a minimum threshold of 12 mA at room temperature under pulse pumping.<<ETX>>

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.

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 VCSELs using AlAs/GaAs mirrors and strain-compensated quantum wells

We present a 1.53 /spl mu/m strain-compensated MQW VCSEL using wafer-fused AlAs/GaAs DBR mirrors. Under room temperature pulsed pumping, we measured excellent dynamic single mode characteristics, a low threshold current of 10 mA, and a linewidth of less than 0.1 nm.

High-performance InGaAs photodetectors on Si and GaAs substrates

In this work, we demonstrate record performance operation of long wavelength (1.55 /spl mu/m) P-I-N (InP-InGaAs-InP) photodetectors on both Silicon and Gallium Arsenide substrates using a wafer bonding technique. The photodetectors were made by first bonding the P-I-N epitaxial layers to the Si and GaAs substrates followed by chemical removal of the host (InP) substrate from the P-I-N structure. The photodetectors were then fabricated atop the newly exposed P-I-N (InP-InGaAs-InP) epilayers. Dark currents of as low as 57 pA on a GaAs substrate and 0.29 nA on a Si substrate were measured under 5 V reverse bias. The responsivity at 1.55 /spl mu/m wavelength was measured to be 1 A/W, corresponding to an external quantum efficiency of 80%. The series resistance measured across the bonded interface and P-I-N layers gave 17 /spl Omega/ on GaAs and 350 /spl Omega/ on Si, respectively.

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/.