Taking on Blue Laser Diodes

Here is an interesting poster presentation made by participants at the recently held Annual Photonics Workshop 2010 in Cochin, India.

One presentation which caught my eye was on the state-of-the-art on blue laser diodes, made jointly by a research scholar at VIT University, Vellore, Tamil Nadu, and a senior lecturer at Government Polytechnic College, Chitradurga, Karnataka.

Nichia, of Japan, is said to be commercializing blue laser semiconductors. GaN-based blue laser diodes with emission wavelength around 405 nm have attracted much interest due to their application in next-generation DVDs.

Applications of diode lasers can be in fiber communications, optical data storage, laser printers, materials and surface treatments, atmospheric sensing, laser ophthalmology, and tissue treatment, surgery, etc.

For heterostructure blue laser diodes, this particular team's work focused on issues such as:

a) reducing the threshold current density, electron leakage and electrostatic fields, and improving the output power;
b) improving the heat removal and estimating the effects of self healing in InGaN/GaN based devices;
c) solving time-independent Schrödinger equation for multiple quantum wells; and
d) studying the material properties of GaN, AlGaN, InGaN, etc.

Some of the possible solutions listed are:

a) Use of AlInGaN electron blocking layer with Al and In compositions properly designed;
b) Increase the cavity length of the laser diode;
c) Use of transfer matrix method;
d) Numerical solutions of Poisson's equation, current continuity equation for electrons and holes, photon rate equation, heat flow equation and wave equation; and
e) Using advanced simulation techniques such as FEM/FDM (nowadays, advanced device simulators are also available like LASTIP, TCAD, COMSOL).

The team aims to develop a blue laser diode model that will overcome all defects. It would also provide guidelines to device engineers for the development of device prototypes that will reduce the experimental trials needed for device optimization.

Blue laser diodes of longer lifetime are said to be in urgent need for the electronics industry. However, this technology is supposedly not yet established as are red lasers. Hence, it presents a lot of scope for young researchers.

The team added that realistic results were possible with careful consideration of material properties.

Pradeep