III-V nitrides - important future electronic materials

The present stage of development for the AlN-GaN-InN class of III-V nitrides is reviewed, with emphasis on the electronic properties of the materials. We also briefly cover the most important types of device structures presently under study, as well as application areas for III-nitride devices now foreseen. A brief overview of the main growth techniques is presented, since a further development of the growth of these materials is indeed the key towards a desired substantial improvement in material quality. This is needed both for the establishment of definite data for physical parameters, as well as for the proper functioning of most devices. The basic band structure as well as excitonic properties are briefly discussed. It is pointed out that these materials are in most cases excitonic at room temperature, for bulk as well as for quantum structures. Doping and properties of donors and acceptors are highlighted, here, in particular, the parameters for shallow acceptors, such as their binding energies, are far from well known. There is no complete picture of the identification of characteristic optical spectra (such as bound exciton spectra) with specific donors and acceptors. The properties of defects, in particular dislocations which are very abundant in the heteroepitaxial material studied today, are discussed. Dislocations may not themselves be severe recombination centers, and the degradation of active devices via dislocation climb seems to be absent in III-nitrides. The progress in the area of heterostructures and quantum wells based on the AlGaN/GaN and the InGaN/GaN systems is reviewed, in relation to the present strong development of related devices. An interesting observation is the importance of the piezoelectric effect, due to a strong built-in strain in most structures. Application areas cover a very broad range in optoelectronics, but also high frequency power devices, with applications for example in satellite communication systems.