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Title: The temperature dependence of the gain in semiconductor lasers
Author: Togher, Paul
ISNI:       0000 0001 3534 4063
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1996
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The work presented in this thesis is involves two distinct topics. The first area is the main theme of the thesis, and is an investigation of the contribution made by the gain to the temperature sensitivity of long wavelength semiconductor lasers. The second topic is in a separate but related area and consists of an experimental determination of the valence band deformation potential, b, whose magnitude is found to be in good agreement with theoretical prediction. The thesis first presents an overview of the equipment used in the measurements, followed by a review of the available methods for making gain measurements on semiconductor lasers. It is concluded that the Hakki-Paoli method, in conjunction with the Cassidy method, provides the most suitable technique, but the measurement system must be very carefully set up to ensure valid results. The gain-current relationship is then measured in three quantum well lasers with 1.55μm tensile, compressive and unstrained active region respectively, and in two 1.3μm devices, with tensile and compressive quantum wells. It has been observed experimentally that the modal gain, G, varies linearly with the log of the drive current, I, in many quantum well lasers. This relationship was expressed by McIlroy as G= Go in011/0 ). It has been suggested that the strong temperature sensitivity of the threshold current in long wavelength lasers is due to strong temperature dependence of the gain characteristics. We show that the Go parameter is virtually independent of temperature in the 1.5μm devices studied, close to that expected for an ideal laser, while the 1.3μm lasers depart from the ideal case to some degree. The 1.54m devices all have a characteristic temperature, To, of = 70K, in good agreement with what would be expected if non-radiative phonon assisted Auger recombination, with an activation energy of 25meV, dominates the current. The lower To values in the 1.3μm devices of 42K and 50K respectively are consistent with an additional temperature dependence of the differential gain above that predicted in an ideal laser. In both cases it is concluded that Auger recombination makes the dominant contribution to the temperature sensitivity. In the second topic considered, photo voltage measurements are used to determine the energy splitting of the light hole and heavy hole valence subbands in a set of tensilestrained lasers. Using these measurements it is shown that a theoretical model, using the interpolated strain deformation potential determined by Krijn, gives good agreement with experiment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Optics & masers & lasers