Electro Optical Characterisation of Short Wavelength Semiconductor ...
CONTENTS 4.2.1 Characterisation of GaN laser diodes . . . . . . . . . . . . . . . . . 42 4.2.2 GaN results in brief . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 5 Summary and Outlook 53 A Electrical Sources & Measuring Devices 55 B ZnSe threshold current density values 57 C Band structure simulation using 1D Poisson-Schrödinger equation solver 59 Acknowledgement 65 2
Chapter 1 Basic Concepts 1.1 Historical Background A thinker sees his own actions as experiments and questions as attempts to find out something. Success and failure are for him answers above all. Friedrich Nietzsche The concept of semiconductor lasers was introduced by Basov et al. in 1961 proposing that stimulated emission of radiation could occur in semiconductors by the recombination of across p − n junction injected carriers . He was rewarded with a Nobel Prize in 1964 for this attempt. In 1962 the first semiconductor lasers appeared in several laboratories independently (Hall et al. ; Holonyak Jr. et al. ; Nathan et al. ; Quist et al. ). All these groups used gallium arsenide, GaAs, in their approaches. Silicon could not be used because of its indirect bandgap although a matured fabrication technology existed. The required direct bandgap materials were found in compound materials which were at that time less understood. The main reasons behind the major surge in role played by semiconductor lasers are their continued performance improvements especially in low-threshold current, ultrashort optical pulse generation, narrow spectral linewidth, high optical output power, low electrical power consumption and low costs. Many of these achievements were based on theoretical understanding of the semiconductor materials and improvement of material growth technologies. In 1969 the heterostructures were introduced . In a heterostructure laser the simple p−n junction is replaced with multiple semiconductor layers of different compositions. The first structures consisted of layers of different compositions of AlxGa1−xAs. Constant wave (cw) operation at room temperature became possible because of better carrier and optical confinement. Laser performance continued to improve as more advanced heterostructures such as quantum wells (QW) were developed. The pioneering works using molecular beam epitaxy i (MBE) (Cho, 1971 ; cho et al., 1976 ; Tsang et al., 1979 ) and metal organic chemical vapour deposition (MOCVD) ii (Dupuis and Dapkus, 1977 ; Dupuis et al., 1978, 1979 [11, 12, 13]) to grow ultrathin semiconductor layers of the order of ten atomic layers, had paved the way for the development of new semiconductor lasers. i epitaxy is Greek formed from ɛπι (on, onto) and τ ´αξη (order) ii alternative names for this process include Metalorganic vapour phase epitaxy (MOVPE), organometallic vapour phase epitaxy (OMVPE) and organometallic chemical vapour deposition (OMCVD) 3
Chapter 5 Summary and Outlook Great
Appendix A Electrical Sources & Mea
ZnSe threshold current density valu
Bibliography  N. G. Basov, O. N.
BIBLIOGRAPHY  G. Snider, 1D Poi