C.J. McLean

Monolithic integration in InGaAs-InGaAsP multiple-quantum-well structures using laser intermixing

The bandgap of InGaAs-InGaAsP multiple-quantum-well (MQW) material can be accurately tuned by photoabsorption-induced disordering (PAID), using a Nd:YAG laser, to allow lasers, modulators, and passive waveguides to be fabricated from a standard MQW structure. The process relies on optical absorption in the active region of the MQW to produce sufficient heat to cause interdiffusion between the wells and barriers. Bandgap shifts larger than 100 meV are obtainable using laser power densities of around 5 W/spl middot/mm/sup -2/ and periods of illumination of a few minutes to tens of minutes. This process provides an effective way of altering the emission wavelengths of lasers fabricated from a single epitaxial wafer. Blue shifts of up to 160 nm in the lasing spectra of both broad-area and ridge waveguide lasers are reported. The bandgap-tuned lasers are assessed in terms of threshold current density, internal quantum efficiency, and internal losses. The ON/OFF ratios of bandgap-tuned electroabsorption modulators were tested over a range of wavelengths, with modulation depths of 20 dB obtained from material which has been bandgap-shifted by 120 nm, while samples shifted by 80 nm gave modulation depths as high as 27 dB. Single-mode waveguide losses are as low as 5 dB/spl middot/cm/sup -1/ at 1550 mm. Selective-area disordering has been used in the fabrication of extended cavity lasers. The retention of good electrical and optical properties in intermixed material demonstrates that PAID is a promising technique for the integration of devices to produce photonic integrated circuits. A quantum-well intermixing technique using a pulsed laser is also demonstrated.

HIGH QUALITY WAVELENGTH TUNED MULTIQUANTUM WELL GAINAS/GAINASP LASERS FABRICATED USING PHOTOABSORPTION INDUCED DISORDERING

Broad area oxide strip lasers have been fabricated from GaInAs/GaInAsP multiquantum well laser material which has undergone various degrees of intermixing by photoabsorption induced disordering. This process provides an effective way of altering the emission wavelength of lasers fabricated from a single epitaxial wafer, and we have demonstrated blue shifts of up to 160 nm in lasing spectra. The band gap tuned lasers are also assessed in terms of threshold current density, internal quantum efficiency, and internal loss and it is shown that good device performance is maintained.

Time-resolved photoluminescence microscopy of GaInAs/GaInAsP quantum wells intermixed using a pulsed laser technique

High spatial resolution time‐resolved photoluminescence has been used to study GaInAs/GaInAsP quantum‐well structures selectively intermixed using the pulsed photoabsorption‐induced disordering technique. Photoluminescence decay measurements at wavelengths ≳1.3 μm were obtained using novel high‐efficiency photon‐counting detectors and were found to correlate spatially with the observed luminescence blue shift in these structures. Results indicate a reduction in the nonradiative recombination time of nearly two orders of magnitude as a result of this intermixing technique.

Fabrication of quantum well photonic integrated circuits using laser processing

Abstract The bandgap of InGaAsInGaAsP multiple-quantum well (MQW) material can be accurately tuned by photo-absorption induced disordering (PAID), using a Nd:YAG laser, to allow lasers, modulators and passive waveguides to be fabricated from a standard MQW structure. The process relies on optical absorption in the active region of the MQW to produce sufficient heat to cause interdiffusion between the wells and barriers. Blue shifts of up to 160 nm in the lasing spectra of both broad area and ridge waveguide lasers are reported. Bandgap tuned electro-absorption modulators were fabricated and modulation depths as high as 27 dB were obtained. Single mode waveguide losses are as low as 5 dB cm−1 at 1550 nm. Selective area disordering has been used in the fabrication of extended cavity lasers. The retention of good electrical and optical properties in intermixed material demonstrates that PAID is a promising technique for the integration of devices to produce photonic integrated circuits. A quantum well intermixing technique using a pulsed laser is also reported.

Direct writing of gratings in GaInAs/GaInAsP quantum wells using pulsed laser irradiation

A new quantum well intermixing technique, which involves irradiating multiple quantum well material with high energy laser pulses and producing transient heating, has been developed. A Q-switched Nd:YAG laser with pulse length of /spl sim/7 ns, repetition rate of 10 Hz and pulse energy density /spl sim/5 mJ mm/sup -2/ is used to generate a localised increase in the density of point defects. After subsequent annealing in a rapid thermal processor bandgap shifts of over 100 nm were observed. The spatial resolution was investigated by masking the sample with a metal mask. Spatially resolved photoluminescence measurements showed that the resolution of the process was 25 /spl mu/m or better, this measurement being limited by the resolution of the photoluminescence set up. Gratings, with a pitch of 2.5 /spl mu/m, were wet-etched into the back of waveguide samples, and the samples were irradiated through the grating and annealed as before. Waveguide transmission spectra showed a dip in the transmitted intensity around a wavelength of 1.525 /spl mu/m indicating that a grating had been formed.

Bandgap tuning of lasers, modulators, and passive waveguides in GaInAsP using photoabsorption-induced disordering

The bandgap of GaInAsP multi-quantum well (MQW) material can be accurately tuned by photo-absorption induced disordering (PAID) to allow lasers, modulators and passive waveguides to be fabricated from a standard MQW laser structure. The bandgap tuned lasers are assessed in terms of threshold current density, internal quantum efficiency and internal losses and exhibit blue shifts in the lasing spectra of up to 160 nm. The ON/OFF ratios of the modulators were tested over a range of wavelengths with modulation depths of 20 dB obtained from material which has been bandgap shifted by 120 nm, while samples shifted by 80 nm gave modulation depths as high as 27 dB. We have also measured single mode waveguide losses over a range of wavelengths and these are 5 dB/cm at 1550 nm. These high quality devices showing good electrical and optical properties after processing demonstrate that PAID is a promising technique for the integration of devices to produce photonic integrated circuits.

Extended cavity lasers fabricated using photo-absorption induced disordering

Photo-absorption induced disordering (PAID) has emerged as a laser induced quantum well intermixing technique of particular applicability to the GaInAsP/InP material system. Blue shifts in the bandgap of >100 meV in standard MQW laser structures are typically obtainable. The spatial selectivity of the technique is, however, limited by lateral heat flow. Here we show that extended cavity lasers can be fabricated by the PAID process, provided the graded interface region is pumped. The PAID process is modelled, and the ultimate spatial resolution is deduced.

High quality wavelength tuned multi-quantum well GaInAs/GaInAsP lasers fabricated using photo-absorption induced disordering

Oxide stripe lasers have been fabricated from GaInAs/GaInAsP multi-quantum well material which has undergone various degrees of intermixing by photoabsorption induced disordering (PAID). Blue shifts of up to 160 nm in the lasing spectra are demonstrated.