J. Beerens

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.

BLUESHIFTING OF INGAASP/INP LASER DIODES BY LOW-ENERGY ION IMPLANTATION

A new method based on low-energy implantation is presented for the fabrication of laser diodes with shifted emission wavelength. The laser diodes are based on InGaAsP/InGaAs/InP material, with compressively strained active layers. Low-energy implantation (18 keV As+) is used to generate vacancies near the surface of an incomplete laser structure, for which the epitaxial growth was interrupted 45 nm above the active layers of the device. The vacancies are subsequently diffused through the quantum wells by rapid thermal annealing. This diffusion causes a local intermixing of atoms at the interfaces of the active layers, which induces an increase of the band gap energy. The implantation/anneal process can be repeated several times to increase the amount of intermixing, thereby further shifting the emission wavelength. Once this process is completed, the upper optical confinement layer of the structure is overgrown using chemical beam epitaxy. Operational lasers with blueshifts as large as 35 nm were obtained.

Blueshifting of InGaAsP-InP laser diodes using a low-energy ion-implantation technique: comparison between strained and lattice-matched quantum-well structures

Blueshifted InGaAsP-InGaAs-InP laser diodes have been fabricated using a technique that includes a low-energy ion implantation, used to generate point defects near the surface of the structure, followed by a thermal anneal which causes the diffusion of these defects through the quantum wells (QWs). This diffusion of point defects induces a local intermixing of atoms in the QWs and barriers, which results in a decrease in the emission wavelength of the devices. Results obtained with strained and lattice-matched QW structures are compared. For lattice-matched structures, electroluminescence wavelength shifts as large as 76 nm were obtained. Strained QW structures presented a much smaller blueshift (/spl ap/10 nm). In both cases, we observed no significant change of the threshold current caused by the intermixing process.

Pulsed photoconductive antenna terahertz sources made on ion-implanted GaAs substrates

In this work we show that improved performances of terahertz emitters can be obtained using an ion implantation process. Our photoconductive materials consist of high-resistivity GaAs substrates. Terahertz pulses are generated by exciting our devices with ultrashort near-infrared laser pulses. The ion implantation introduces non-radiative centres, which reduce the carrier lifetime in GaAs. The presence of the charged defects also induces a redistribution of the electric field between the antenna electrodes. This effect has a huge influence on the amplitude of the radiated terahertz field. Results obtained as a function of the laser excitation power are discussed and a comparison of the performance of these devices with a conventional antenna-type emitter is given.

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.

Γ‐X intervalley transfer in single AlAs barriers under hydrostatic pressure

We have investigated the contribution of Γ‐X intervalley transfer to the tunneling current in single AlAs barrier heterostructures grown on a GaAs substrate by measuring I‐V characteristics at low temperature and under hydrostatic pressure up to 9 kbar. The application of hydrostatic pressure affects the contribution of the Γ‐X transfer process to the total tunneling current at a given bias voltage. Experimental results are compared with current‐voltage characteristics calculated with a model taking into account the Γ‐X transfer at heterointerfaces. Only transfer processes involving the longitudinal X valley in AlAs are considered in the calculations. Very good agreement is found for low bias conditions at all pressures.

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.

Monolithic intracavity laser-modulator device fabrication using postgrowth processing of 1.55 μm heterostructures

In this letter, we present the attractive characteristics of a fabrication method based on quantum-well intermixing induced by low energy ion implantation for the realization of photonic integrated circuits on GaInAsP–InP heterostructures. Intracavity electro-absorption modulators monolithically integrated with laser devices were fabricated, using this postgrowth technique. The modulator section of the integrated devices was blueshifted by 75 nm while keeping the laser section unshifted and preserving very low values of the lasing threshold current density. Modulation depths in excess of 10 dB/V at 1.55 μm were obtained on these integrated devices which incorporate both a modulator and a laser.

Photoconductivity and photoluminescence of GaAs grown on Si by molecular beam epitaxy

Abstract Photoconductivity (PC) and photoluminescence (PL) have been used to characterize GaAs grown on Si (100) by molecular beam epitaxy. The GaAs layers are known to be under biaxial tensile strain because of the difference in the thermal expansion coefficients of GaAs and Si. This strain is responsible for the splitting between heavy- and light-hole valence bands and could be monitored via the electron to heavy-hole (e-hh) and electron to light-hole (e-lh) transitions. These two transitions are observed in both PL and PC spectra. The stress present in the GaAs layer is calculated to vary from 1.8 kbar at room temperature to 2.7 kbar at 4.2 K. It is also shown that the temperature evolution of the stress as a function of temperature is entirely controlled by the difference between the thermal expansion coefficients of the two materials.

Dependence of conduction‐band effective mass on quaternary alloy composition of (In0.52Al0.48As)z(In0.53Ga0.47As)1−z lattice matched to InP

Cyclotron resonance measurements were carried out on high quality (In0.52Al0.48As)z(In0.53Ga0.47As)1−z thick layers grown on InP substrates by molecular beam epitaxy. The measurements were performed at 60 K and we were able to obtain the electron effective mass dependence with z in the whole range of composition 0≤z≤1. Using the band‐gap values as obtained from photoluminescence measurements on the same samples at 60 K, nonparabolicity corrections were taken into account to obtain the effective mass m0* at the conduction band edge. A nonlinear variation m0* with z could be inferred from our experimental data. The expression m0*(z)/me=0.043+0.042z−0.016z2, which includes a quadratic dependence in z (or a so‐called bowing parameter), gives a very good fit to our experimental data.