Metamorphic Heterostructures and Lasers on GaAs

Doctoral thesis, 2008

The objective of this thesis is to demonstrate the metamorphic growth of heterostructure lasers on GaAs substrates. Many heterostructure devices have their performance limited by the need to grow on lattice-matched substrates. Metamor phic growth is a method of producing semiconductor heterostructures on virtual substrates with arbitrary lattice constants. Our approach is to use an alloy graded InGaAs buffer layer to bridge the gap between the GaAs substrate and the virtual substrate. To put the metamorphic technique into perspective, we present a number of other methods for fabrication of heterostructures that are not lattice-matched to standard substrates. There is also a discussion on metamorphic growth in other material systems than InGaAs/GaAs. Metamorphic devices are already on the market in the form of high-electron mobility transistors, HEMTs. However, the development of metamorphic optoelectronic devices has been much slower. The development of fiber-optical networks for broad-band access creates a market for low cost laser transmitters in the 1.3-1.55 µm wavelength range. The existing InP-based lasers have problems with poor thermal stability and are not compatible with the high reflectivity GaAs/AlAs distributed Bragg reflector technology for making vertically emitting devices. The performance of such lasers could be improved by using GaAs-based devices, e.g. highly strained GaInNAs(Sb) quantum wells (QWs), InAs quantum dots (QDs) or metamorphic QWs or QDs. By using metamorphic growth it is possible to produce different virtual substrates for 1.3 and 1.55 µm to give optimum performance of the laser. In the appended papers we successfully demonstrate InGaAs QW lasers grown on GaAs, with pulsed operation in the range 1.25-1.58 µm as well as continuous operation at 1.33 µm, all at room-temperature.