Abstract
Multiple quantum well lasers based on the III-V compound semiconductor indium phosphide were studied in this thesis. Systematic investigations were carried out on the effects of quantisation and strain on the temperature sensitivity of threshold current, modulation properties, external cavity operation and the 'gain lever' effect. Trends in the temperature sensitivity of threshold current for lasers of various lengths and quantum well numbers can be understood in terms of the nonlinear gain-current density relation. However, compared to bulk active region devices there was no significant improvement. It is unclear at present whether this is due to the temperature sensitivity of optical gain or Auger recombination. Relative intensity noise measurements were used to compare the modulation properties of lattice-matched and strained MQW lasers. This method gives an estimate of the differential gain and was used to study the properties of devices which were unsuitable for high speed applications. These measurements showed that gain saturation and carrier transport effects may be significant in certain laser structures. Band-filling effects due to the reduced volume and modified density of states were utilised in the demonstration of a grating external cavity laser operating across the 1.3 mum optical fibre window. This configuration results in single-mode operation across the gain spectrum of the laser. High output power was exhibited across a wide tuning range. The 'gain lever' effect uses the nonlinear gain-current density relation to enhance the amplitude modulation efficiency and the signal-to-noise-ratio. MQW and bulk devices of different length and split ratio were compared. It was seen experimentally and numerically that the nonlinearity causing this effect also increases the distortion. Finally, it is discussed that further modifications to laser properties may be seen in active regions incorporating quantum wires and boxes.