III-Nitride QD Lasers

Abstract

III-Nitrides QD lasers are studied in detail. Two types of QD structures are considered, GaN/AlxGa1-xN/AlN and InxGa1-xN/ In0.04Ga0.96N /GaN. Effects of: QD size; QD and WL composition; and doping are studied through the cal- culations of gain, threshold current, and intensity modulation bandwidth. It is shown that GaN QDs are less sensitive to size fluctuations. Bandwidth increases with doping and reducing QD size. The study covers approximately (300-600 nm) wavelength range. I. INTRODUCTION Semiconductor nitrides are very promising materials for their potential use in optoelectronic devices and high- temperature electronic devices. Until few years ago, the commonly quoted value for the optical bandgap of InN was 1.89 eV (1), but new measurements have shown evidence of a much smaller bandgap between 0.65 and 0.9 eV (2, 3). The energy range of III-nitride (III-N) alloys from 6.2 eV (pure AlN) to 0.7 eV (pure InN) covers the spectral range from deep ultra violet (UV) to infrared (IR) at room temperature. These materials are thus, suitable for applications in UV de- tectors, Bragg reflectors, waveguides, and UV and visible light emitting diodes (LEDs). GaN-based LEDs and LDs have been achieved using thin films or QWs (1). Develop- ment Laser diodes (LDs) of LDs with quantum dots (QDs), for example, is expected to result in a lower threshold cur- rent (4). To access the advantages of QDs, the maximum size of QDs must be on the order of a few nanometers as a Prequisite for utilization zero-dimensional confinement. With such small size, the practical applications are thus often associated with a large assembly of QDs rather than a single one. This implies that the size uniformity of the dot assembly is critical. Fluctuations in dot size produce an inhomogene- ous broadening in quantized energy levels and may destroy the very properties expected from a single QD. Fabrication of a QD assembly with small and uniform size, high density, well-ordered placement, and defect-free materials today re- mains a serious challenge in any semiconductor system, es- pecially when using III-N materials. The properties of III-N QDs are closely related to those of bulk materials that have been reviewed in many articles (5). Although bulk GaN, AlN, and InN can all crystallize in wurtzite, zinc blende, and rock salt structures, in ambient conditions, the thermody- namically stable structure, however, is the wurtzitic phase. III-nitride QDs are commonly the strained systems. The lat- tice mismatch and its induced strain have a profound effect on the growth, structures, and properties of semiconductor QDs.