Design And Optimization Of Multi--Quantum \\Tells For Gaas Based Vertical Cavity Surf Ace Emitting Lasers
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Date
2011-01
Authors
Jasim, Farah Z
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Device simulations for the electrical and optical characteristics of GaAs based
vertical cavity surface emitting lasers (VCSELs) have been investigated. In such lasers,
carrier's leakage and lateral current separation are some of the major problems in
VCSEL design. Thus, in this work the design of VCSEL structures including multi
quantum wells (MQWs) active region are described and investigated by Integrated
System Engineering Technology Computer Aided Design (ISETCAD) device simulator.
The parameters of VCSEL structures are varied and optimized for high performance.
This optimization study involves aspects such as the number of distributed Bragg
reflectors (DBRs) pairs, thickness of quantum wells, wells number, doping of the DBR
pairs, thermal characteristics and several approaches to improve and achieve high
efficiency, low threshold current and high output power.
In order to enhance the device performance and reduce carrier leakage in~ide the
VCSEL cavity, a new model is proposed where three pairs of both p and n-type DBRs
nearest to the active region, and which are in the proximity of the spacer are doped at
5xl0+17cm-3 and the rest are doped highly at IxlOt-19 cm-3 concentration. In this case,
better matching of carrier distribution of the DBRs and the spacers can be achieved. An
output power of 12.7 mW, threshold current of 280 J.lA, and the outer voltage of 2.5 V
were obtained from cylindrical structure with radius of 2 Jlm. The output slope
efficiency and differential quantum efficiency (DQE) are the key performance
parameters of the VCSEL. Slope efficiency of 0. 999 and DQE up to 0.683 at an
emission wavelength of 848.30 nm are achieved. This is essentially a very important
aspect to be considered for the device fabrication.
Large area of VCSELs designs result in multimode operation. A new design is
proposed to enhance single fundamental mode with low threshold current operation at
higher output with two oxide confined (OC) apertures VCSEL. It was observed that
when two apertures with radius of 4.2 11m were added to the node position of the
resonator standing wave, single fundamental mode was achieved as well as the threshold
current was decreased from 1. 77 to 1.67 mA.
Description
Keywords
GaAs based vertical cavity surface , emitting lasers.