Piezoelectric indium gallium arsenide/gallium arsenide strained quantum well structures on (111)A gallium arsenide: MOVPE growth, properties, and application to semiconductor lasers

Strained InGaAs/GaAs quantum well (QW) structures on <111>-oriented substrates have received considerable attention because of the existence of a strong{09} piezoelectric (PE) field in the wells and also their unique optical and electrical properties. In order to exploit the unique properties of <111> QW structures for device applications it is necessary to achieve high crystalline and interfacial quality and to determine their physical properties. Therefore, the challenge was to achieve the appropriate growth conditions for <111> strained QW structures and to understand their structural and physical properties.; This thesis focuses on achieving high quality [111]A-oriented strained InGaAs/GaAs/AlGaAs QW structures grown by metalorganic vapor phase epitaxy (MOVPE) and to investigate their physical properties for application to devices exploiting the large PE field. For this purpose the MOVPE growth and properties of [111]A InGaAs/GaAs QW structures were extensively studied, especially for InGaAs/GaAs/AlGaAs double confinement QW structures embedded in P-I-N and N-I-P configurations. Also, PE laser diodes were fabricated using these strained QW structures and characterized. The quality of the QW structures was investigated by means of photoluminescence (PL) spectroscopy, high resolution X-ray diffractometry, and transmission electron microscopy (TEM). The growth conditions were determined to obtain pseudomorphically strained structures with excellent interfacial characteristics and uniformly strained structures with no compositional modulation for [111]A-oriented QWs with well widths of 65–110 Å containing up to ∼25% In both for undoped and P-I-N (or N-I-P) doped configuration heterostructures. Well width fluctuation values of [111]A QWs are in the range of ±(1–2) monolayers (ML) even for a highly strained QW with 25% of In, while larger fluctuations were observed for simultaneously grown [100]-oriented structures. Also, the critical layer thickness (CLT) for [111]A strained structures was experimentally investigated and compared with the theoretically expected CLT, which shows that the CLT for [111]A strained structures is larger than for [100] structures. In order to have complete P-I-N and N-I-P device structures, we obtained the growth conditions for highly doped GaAs and AlGaAs layers using Si and C as n-type and p-type dopants, respectively. Especially, Si-doped n-type GaAs layers on (111)A substrates were studied in detail. P-I-N laser diodes were fabricated by a conventional stripe laser fabrication process. From an analysis of the different band profiles for P-I-N and N-I-P structures considering the direction of the PE field, we found that P-I-N lasers may have an advantage in carrier confinement for [111]A-oriented structures. Room temperature laser operation was achieved at a wavelength of ∼1.0 μm with a threshold current density of 780 A/cm2 for a 850 μm long cavity with a 40 μm stripe. This is the first demonstration of [111]A PE laser diodes. The successful demonstration of this PE laser not only provides further evidence of the very high quality of the InGaAs/GaAs/AlGaAs heterostructures grown on (111)A GaAs by MOVPE, but also shows good possibilities for other novel devices exploiting the PE field in these strained structures.