Tesis:
GAAS-BASED QUANTUM WELL AND QUANTUM DOT LIGHT-EMITTING DIODES AND LASERS FOR 1.3 AND 1.55 MICRO-M EMISSION.
- Autor: MONTES BAJO, Miguel
- Título: GAAS-BASED QUANTUM WELL AND QUANTUM DOT LIGHT-EMITTING DIODES AND LASERS FOR 1.3 AND 1.55 MICRO-M EMISSION.
- Fecha: 2010
- Materia: Sin materia definida
- Escuela: E.T.S. DE INGENIEROS DE TELECOMUNICACION
- Departamentos: INGENIERIA ELECTRONICA
- Acceso electrónico: http://oa.upm.es/4025/
- Director/a 1º: HIERRO CANO, Adrián
- Resumen: The goal of this thesis is the research of new materials for the fabrication of light-emitting devices based on GaAs for operation at the second and third optical fibre telecommunications windows, at wavelengths around 1.3 and 1.55 µm, respectively, using GaInNAs/GaAs quantum wells (QWs) and InAs quantum dots (QDs). GaInNAs/GaAs QWs. In this part, a series of laser diodes is presented from which, by varying the N content in the QW, laser operation from 1 to 1.5 µm is achieved. The increase in N concentration also results in a degradation of the threshold current density, J_th, and a decrease of the external differential quantum efficiency, eta_d. It is shown that the origin of this degradation is a decrease of the internal quantum efficiency, eta_i, with the addition of N, and an increase of the optical losses of the cavity, alpha_i, and the transparency current density, J_tr, with the N concentration. Moreover, it is shown that the characteristic temperatures of J_th and eta_d, T_0 and T_1, respectively, tend to degrade as the N content increases. The degradation of T_0 is mainly due to the increase of alpha_i, and a decrease of the modal gain, Gamma g_0, and the characteristic temperature of J_tr, T_tr. In turn, the increase of alpha_i is the main responsible for the degradation of T_1. A calculation of the effective lifetime of carriers in the QW and its temperature dependence, allows to rule out carrier leakage from the QW as the dominant process limiting T_0 and T_1. Finally, an analysis of the role played by the differential carrier spreading efficiency, eta_s, on the degradation of eta_i is performed. Firstly, it is found that J_th is strongly dependent on the current injection location in N-containing diodes, due to a poor carrier spreading along the length of the laser diodes. Secondly, the above-threshold Fermi level pinning in the QW is analysed. Based on these results it is found that eta_s degrades by a ~16% upon addition of N. This degradation can explain part of the previously found degradation by ~35% of eta_i with the addition of N. On the other hand, the figures of merit of a series of GaInNAs/GaAs QW-based resonant cavity light-emitting diodes emitting at 1.3 µm are studied as a function of the growth temperature of the distributed Bragg reflectors (DBRs) which define the cavity, and as a function of the alloying of the electrical contacts. It is found that the external efficiency, eta_ext, the width of the electroluminescence (EL) peak, and the I-V characteristics of the diode degrade as the DBR growth temperature decreases. The best results have been obtained when such temperature is 750 ºC and the metallic contacts are not alloyed. InAs QD-based LEDs. Firstly, room-temperature EL at 1.5 µm is demonstrated from LEDs based on InAs QDs covered by Ga_0.85In_0.15N_0.02As_0.98. The incorporation of N results in a degradation of eta_ext, which can be partially alleviated if the devices are subjected to a post-growth rapid thermal annealing, although this process also results in a blue-shift of the emission wavelength. The second strategy consists on covering these InAs QDs with a GaAsSb capping layer. Thus, room-temperature EL at wavelengths between 1.1 and 1.5 µm is obtained. The value of eta_ext increases with the Sb content in the capping layer until a concentration of this element of ~14% at which eta_ext decreases. That is the Sb concentration at which the band alignment between the QDs and the capping layer changes from type I to type II, as confirmed experimentally through the observation of the EL peak wavelength blue-shift as a function of the injected current. This series of LEDs shows much higher values of eta_ext than the InAs/GaInNAs-based series in all the wavelength range considered.