This thesis explores carrier trapping and recombination indefect-rich semiconductors, and methods for materialcharacterisation. Optimal manufacturing parameters areestablished for materials to be used in the ultrafast devicesneeded for future telecommunication applications. Thesemi-insulating properties and ultrashort carrier lifetimes inthe investigated materials are due to the efficient trapping ofcarriers to centers with their energy levels deep within theband gap of the material. The carrier recombination processesin the investigated materials are studied with time-resolvedphotoluminescence (TRPL) and dynamic transmission (DT)/reflection (DR) measurement techniques. Analysis of several ofthe measurements are performed using computer simulation of theexperiments. The simulations are based on rate equation modelsof the carrier populations in the conduction band, valenceband, and at the deep centers.
Investigations were made on InP:Fe, GaAs:Fe and GaInP:Feregrown on semiconductor planar lasers and vertical cavitysurface emitting lasers using hydride vapour phase epitaxy. Thecharacterisation was made by TRPL, and by focusing theexcitation beam to a nearly diffraction limited spot size aspatial resolution of about 1 µm was obtained. It wasfound that despite variations in growth velocity and morphologywithin the regrown layers, the semi-insulating properties aremaintained everywhere, even in the critical region close to thelaser mesa where leakage current is most likely to occur.
A TRPLand DT/DR study of Be-doped low-temperature-grown GaAshas also been undertaken to investigate the effects ofannealing and Be concentration on the ultrafast carriertrapping properties of this material. The electron trappingtimes in this material vary from tens of femtoseconds up to afew picoseconds, depending on the Be doping and annealingconditions. Optimal fabrication parameters are presented foruse in ultrafast optoelectronic devices. TRPLand DR was used tocharacterise implanted and annealed InP and In- GaAs for use infuture Tbit/s telecommunication applications. Optimalfabrication parameters are presented also for thesematerials.
Carrier dynamics in aligned InAs/GaAs quantum dots grown ondislocationinduced patterns was studied with TRPL. Shortcarrier lifetimes in the dots indicate effective nonradiativerecombination through point traps near the dots. A proposal onthe nature of the carrier traps is given.
Stockholm: Fysik , 2003. , vii, 76 p.