Growth of indium gallium arsenide/gallium arsenide self-organized quantum dots and their application to high-speed lasers and spin-polarized light sources.

Abstract

In the past few years, self-organized QDs have been extensively investigated to incorporate dots in the active region of optoelectronic devices such as lasers, modulators, and detectors. In the first part of my research, the structural, electronic and non-linear optical and electro-optic properties of the (In,Ga)As QDs were investigated. We determined a conduction band-offset of about 340 meV in InAs/GaAs QDs, which agrees very well with theoretical predictions. The non-linear electro-optic properties of the QDs were studied using a waveguide type structure and linear electro-optic coefficients in InGaAs/GaAs QDs were measured to be larger than LiNbO₃. Following this, I did temperature dependent large-signal and small-signal modulation measurements on SCH single-mode QD lasers to understand the carrier dynamics and properties of hot carriers in QDs. From the small-signal modulation measurements it was evident that there is a significant gain compression at the lasing energy in SCH QD lasers. To overcome this gain compression, primarily due to the presence of hot carriers, we injected electrons into QDs by tunneling to demonstrate the <italic>first</italic> room temperature tunnel injection (TI) QD laser with modulation bandwidth over 20GHz. We have also measured T0 values in excess of 350K upto 60&deg;C and in excess of 200K in the temperature range 60&deg;C < T < 120&deg;C. These devices are also characterized by high quantum efficiencies, low chirp and low linewidth enhancement factor. In the final section of my work, diluted magnetic semiconductors: (Ga,Mn)As and (In,Mn)As for their application to spintronics were developed. We reported the <italic>first</italic> spin-polarized In_0.4Ga_0.6As/GaAs QD surface-emitting diode with a Ga_0.974Mn_0.026As spin injector layer. Spin-polarized holes from this ferromagnetic layer recombine with electrons in the QDs to produce circularly polarized light output. The peak optical polarization efficiency at 5.1K is 18%. We also studied and characterized (In,Mn)As self-organized diluted magnetic quantum dots (DMQD) grown. We measured a Curie temperature, T_c, as high as 150K in the quantum dot layers with 5% nominal Mn content. The high T_c values are explained by a model taking into account a random distribution of Mn composition amongst the dots. Hysteresis behavior in the magnetization confirms the ferromagnetism in the dots.