Research in Electronic and Optoelectronic Materials and DevicesJon M. Pikal, Assistant Professor of Electrical and Computer EngineeringPh. 307-766-3172 E-mail: jpikal@uwyo.edu |
Investigation of charge carrier processes in semiconductor materials and
device, specifically carrier capture,
escape and recombination in semiconductor lasers. The
studies center around understanding the temperature
dependence of the threshold current in long wavelength and
optimization of laser materials and structure design.
Students:
Note: Teaching and research assistanships
for graduate students in the Electronic and Optoelectronic
Materials and Devices area are available. For more information
contact Dr. Pikal by e-mail (jpikal@uwyo.edu)
.
Research Projects:
Semiconductor lasers are important devices found in many of today’s commercial and military communication systems. These systems typically use optical fiber for the transmitting media allowing for high bandwidth transmission free from electromagnetic interference. The primary wavelengths of interest for these systems are 1.3 um and 1.5 um, as these correspond to the zero dispersion and minimum loss of silica fiber, respectively. Several important problems exist in current long wavelength lasers. The strong temperature dependence of the threshold current necessitates active cooling of the laser, increasing the size, cost, and power requirements of the system. In addition, these lasers are currently made on InP substrates making it very difficult to produce the vertical cavity surface emitting lasers (VCSELs) needed for optimum coupling into optical fiber.
The use of InGaAs/GaAs quantum dot active regions can have an impact on both of these problems. Because the quantum dots are grown on a GaAs substrate, current technology for AlAs/GaAs distributed Bragg reflector mirrors and selective oxidation can be used. In addition, the modified density of states of the quantum dot may dramatically reduce Auger recombination, which is one of the major causes of the temperature dependence of the threshold current in current 1.3 um lasers. While room temperature lasing at 1.3 um has been achieved, a great deal of work is needed to understand the operation of these devices in hopes of optimizing their performance.
The goal of this project is to quantify the importance of the different recombination processes both radiative and non-radiative that contribute to the threshold current in long wavelength Quantum Dot (QD) lasers. The significance of this work is that from measurements of these basic laser properties, and their temperature dependence, we will gain information on the operation of these important quantum dot devices leading to improvements in the design and performance of long wavelength semiconductor lasers. In addition, the measurement and analysis techniques developed in this work will be applicable to quantum dot lasers emitting at other wavelengths.
A study of the effect of the bias current dependence of the internal injection efficiency on the determination of the carrier recombination coefficients in semiconductor lasers. The recombination coefficients are found from a fit of the measured carrier lifetime as a function of bias current using a model that assumes a constant internal injection efficiency. From theory we know that the injection efficiency is not a constant. The constant efficiency assumption thus adds error to the determination of the recombination coefficients. The goal of this project is to determine the bias dependence of the injection efficiency and include this in our calculation of the recombination coefficients. We will determine the internal injection efficiency from the measured spontaneous emission spectra and the above-threshold slope efficiency of the semiconductor laser. A comparison can then be made between the recombination parameters obtained using both the constant and bias dependent efficiency to determine the importance of this effect.