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

Qiu, Bocang (1998) Photonic integration in InGaAs/InGaAsP multiple-quantum well laser structures using quantum well intermixing. PhD thesis, University of Glasgow.

Abstract

The damage introduced into an InGaAs/InGaAsP quantum well structure during CH4/H2
reactive ion etching (RIE) processes was measured, for plasma powers from 20 W to 100 W,
using low temperature photoluminescence. The damage depth profile is estimated to be
around 12 nm - 70 nm after annealing at 500 °C for 60 seconds using a rapid thermal
annealer (RTA). A reduced damage RIE process has been developed to fabricate
InGaAs/InGaAsP multi-quantum well ridge waveguide lasers. The performance of these
lasers has been compared to that of lasers fabricated from the same epilayer using wet
etching to form the ridge. The resultant threshold currents were essentially
indistinguishable, being 44.5 mA and 43 mA respectively for dry and wet etched lasers
with 500 μm long laser cavities.
Quantum well intermixing in the InGaAs/InGaAsP material system was demonstrated using
two techniques. The first was a laser irradiation process, which combines irradiation by
continuous wave and Q-switched pulsed Nd: YAG lasers. Differential shifts up to 70 nm have
been obtained. The second was a plasma process which involves sputtering a thin layer of
Si02 and subsequent high temperature annealing using either a CW laser or rapid thermal
annealer (RTA). Differential blue-shifts of the bandgap of up to 120 nm were obtained.
The bandgap shift in the control regions is very insignificant. Measurement of the spatial
selectivity of this technique shows that the spatial resolution is better than 50 μm.
The design, fabrication and characterisation for 3-dB MMI couplers were carried out using
both as-grown (peak emission wavelength of 1.48 μm) and bandgap widened material. The
measured results show good agreement with the design. A splitting ratio of around 0.12 dB
(51: 49) has been achieved for an MMI section length of 470 gm.
Low loss waveguides have been fabricated using the laser process. A loss as low as
2.1 dB/cm was obtained for an operation wavelength of 1.556 um.
Extended cavity ridge lasers (ECL) in InGaAs/InGaAsP multiple-quantum well structures
have been successfully fabricated using the two QWI technique developed. The increases in
threshold current were only 10 mA and 8 mA for cavity length of 800 4m active section
and 1000 μm passive section, compared to the all active lasers with cavity length of 800 μm,
and the losses in the passive sections of ECLs were calculated which were 2.4 cm-1 and
4.4 cm-1, for the two processes, respectively. Considerable theoretical work was carried out, which included the calculation of the optical
confinement and gain in the InGaAs/InGaAsP MQW structure used throughout this thesis.
Modelling of the intermixing of quantum wells was also performed and the results indicate
that the changes of bulk bandgap energy are mainly responsible for the blue-shift of the
photoluminescence.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Marsh, Prof. John
• Date of Award: 1998
• Depositing User: Ms Mary Anne Meyering
• Unique ID: glathesis:1998-6887
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2015 16:19
• Last Modified: 02 Dec 2015 10:30
• URI: https://theses.gla.ac.uk/id/eprint/6887