H.S. Lim

Low-energy ion-implantation-induced quantum-well intermixing

In this paper, we present the attractive characteristics of low-energy ion-implantation-induced quantum-well intermixing of InP-based heterostructures. We demonstrate that this method can fulfil a list of requirements related to the fabrication of complex optoelectronic devices with a spatial control of the bandgap profile. First, we have fabricated high-quality discrete blueshifted laser diodes to verify the capability of low-energy ion implantation for the controlled modification of bandgap profiles in the absence of thermal shift. Based on this result, intracavity electroabsorption modulators monolithically integrated with laser devices were fabricated, for the first time, using this postgrowth technique. We have also fabricated monolithic six-channel multiple-wavelength laser diode chips using a novel one-step ion implantation masking process. Finally, we also present the results obtained with very low-energy (below 20 keV) ion implantation for the development of one-dimensional and zero-dimensional quantum confined structures.

A novel fabrication technique for multiple-wavelength photonic-integrated devices in InGaAs-InGaAsP laser heterostructures

We report the fabrication of multiple wavelength chips in InGaAs-InGaAsP laser structure using a novel ion implantation induced quantum-well (QW) intermixing technique. This technique first consists of using a gray mask photolithography and reactive ion etching process to create a SiO/sub 2/ implant mask with variable thickness on the sample. This is followed by a single 360-keV phosphorus ion implantation at a dose of 1/spl times/10/sup 14/ cm/sup -2/ at 200/spl deg/C, which creates different amounts of point defects in the sample depending on the local thickness of the SiO/sub 2/ mask. A subsequent thermal annealing step induces QW intermixing through the diffusion of the point defects across the structure. With this technique, we have successfully fabricated 10-channel multiple wavelength laser diodes, with lasing wavelength spreading over 85 nm (between 1.47 and 1.55 /spl mu/m), monolithically integrated on a single chip. Only a limited increase of threshold current density of 17% (i.e., from 1.2 to 1.4 kA/cm/sup 2/), has been observed between the least intermixed and the most intermixed lasers.

Generation of Multiple Energy Bandgaps Using a Gray Mask Process and Quantum Well Intermixing

We report a technique for generation of multiple energy bandgaps using a combination of one-step gray mask lithography and low-energy arsenic ion implantation induced disordering. Using this technique, we have successfully integrated 12-section with variable energy bandgaps on a single InGaAs/InGaAsP laser heterostructure. When compared to conventional processes, this novel technique is simple, promising and cost effective.

Multiple-wavelength operation of electroabsorption intensity modulator array fabricated using the one-step quantum well intermixing process

Multiple-wavelength selective channel electroabsorption intensity modulators have been fabricated on a single InGaAs/InGaAsP chip using a one-step quantum well intermixing process. This technique was demonstrated for tailoring the intensity modulator operating wavelength by incorporating low-energy (360 keV) phosphorus ions implantation induced disordering process with gray-mask lithography technology. A modulation depth of −15 dB has been measured from these devices with a voltage swing of −4.5 V.

Effect of etch pit density of InP substrate on the stability of InGaAs/InGaAsP quantum well laser materials

InGaAs/InGaAsP quantum well structures have wide applications, such as the integration of optoelectronic devices and low threshold current density laser, as well as low loss waveguides and optical switching elements. In many case, high temperature operations are necessary during the course of processing a wafer. Here, we report the influence of low and high etch pit densities (EPD) InP substrates on the thermal stability of InGaAs/InGaAsP quantum well laser structure. Both the n-type of S-doped (EPD<500 cm-2)and Sn-doped (EPD≈5x104cm-2) InP substrates were grown under the same run with half wafer each. To assess the thermal stability, the samples were annealed, using a rapid thermal processor, between 650 °C and 750 °C, for 60 seconds. 77 K photoluminescence measurements were performed on the samples after annealing to study the degree of bandgap shift. It was found that S-doped InP substrate with low EPD, i.e. low point defect density, is thermally stable up to an annealing temperature of 625 °C for 60 seconds. Compared to the S-doped materials, laser structure grown on the Sn-doped InP substrate was found to exhibit larger degree of bandgap shift resulted from defects induced quantum well intermixing.

Impact of quantum well intermixing on polarization anisotropy of InGaAs/InGaAsP quantum well modulators

This article reports on the impact of the induced strain on the polarization anisotropy of a parallel set of electroabsorption intensity modulators on a single InGaAs/InGaAsP wafer chip. The strain build up due to the interdiffusion of atomic species across the quantum well region has been demonstrated experimentally using the gray mask-based quantum well intermixing process followed by an annealing step. A voltage swing of 5 V and an intensity modulation depth of more than −15 dB has been measured from these modulators. An interdiffusion process modeling has been developed to investigate the consequence of different interdiffusion ratios between the group III and the group V sublattices on the polarization behavior of these modulators, owing to the strain build up and the refractive index profiles for both transverse electric and transverse magnetic modes. The numerical modeling agrees with the experimental results, which indicates that the degree of intermixing on the group V sublattices is more signifi...

Polarisation-dependent performance of multiple wavelength electro-absorption intensity modulator arrays on a single InGaAs/InGaAsP chip

We report the fabrication of 10-channel electro-absorption (EA) modulator arrays using a lattice-matched InGaAs/InGaAsP MQW structure. The fabrication method is based on the combination of using gray mask lithography and a low-energy arsenic (As) ion-implantation induced disordering (IIID) process. To understand how the QWI process may affect polarisation performance, a theoretical model based on different rates of group III and group V interdiffusion has also been developed.

Multiple-channel InGaAs/InGaAsP electro-absorption intensity modulator fabricated using low-energy-phosphorus-ion-implantation-induced intermixing

A new quantum-well intermixing process in InGaAs-InGaAsP structures, based on controlled low energy phosphorus (P) ion implantation, has been employed in the fabrication of multiple wavelength selective channel electroabsorption (EA) intensity modulators. These modulators, fabricated on a single chip, have an intensity modulation depth as high as -1 1 dB for voltage swings as low as -6 V.

Photonic integration of InGaAs/InGaAsP laser using low energy arsenic implantation induced disordering for quantum well intermixing

Quantum well intermixing (QWI) using a neutral impurity induced disordering technique is of great interest in producing photonic integrated circuits (PICs). We report a high selectivity QWI process using a low energy arsenic implantation induced disordering technique. Since it is known that free electrons from impurities result in high optical absorption and degrade the quality of the material after intermixing, arsenic, an electrically neutral species in the InGaAs/InGaAsP system, was chosen for the process development. The relatively low implantation energy, 360 keV, reduces the damage generation and results in a shallow implantation depth far away from the active region. We have successfully blue shifted quantum well laser material with a control on the amount of intermixing by varying the dose of As implantation at 200/spl deg/C. A wide range of differential bandgap shifts going up to 60 meV are reported. PICs such as extended cavity lasers and monolithic multiple wavelength laser sources are currently being investigated using this technique.

A low-cost solution in generating multiple-bandgaps for 1.55 /spl mu/m optical fibre communications

We have demonstrated that a novel masking technique for low energy quantum well intermixing (QWI), comparable to selective area epitaxy, can be used for the realization of multiple bandgaps in the production of WDM quantum well laser sources, as well as other photonic integrated circuits for use in 1.55 /spl mu/m optical fibre communications applications.