Applications of semiconductors laser in high-pressure studies

Abstract

Advances in Diamond Anvil Cell (DAC) technique have enabled a variety of condensed matter physics studies to be performed at very high pressure, up to -56O GPa. Valuable information on phase stability, EOS, band structure and metal to insulator transition has been obtained on a large number of semiconductors. The introduction of the laserheating technique has opened up a new era in high-pressure, high-temperature research, for experiments that were previously possible only through shock wave techniques. This technique is presently being exploited to synthesize novel materials hitherto only theoretically predicted. The search for metallic hydrogen is still on, and DAC experiments under low temperature and high pressure have been performed to draw the phase diagram of hydrogen. A question that is paramount in every mind concerns the ultimate structure of condensed matter [1,2]. Many elemental systems appear to adopt the body-centered cubic phase. Further many elemental insulators and semiconductors turn metallic at high pressures. Very recently sulfur has been shown to become metallic and superconducting near 93 GPa [3]. This suggests that elements such as Br, Cl may turn metallic at pressures reachable today with the diamond anvil cell. Improvements in DAC capability (up to ~56O GPa), the fabrication of micro X-ray beams (~3 µm), coupling the DAC with the SRS (brilliance ~1015 photons/s/mrad/100mA/0.1%??/?), the possibility of laser heating (~7000 K) simultaneously with pressure, and the advances in area detectors such as the imaging plate system and charged-coupled devices open up new areas for semiconductor physics research that need to be judiciously exploited. For DAC electrical resistivity work, a tough problem has been in attaching good ohmic contacts to the sample. The mechanical contacts often used for performing measurements on bulk would severely degrade the device properties of the heterostructure. Until advancement occurs in this area, the information obtained through electrical resistivity, Hall mobility, and thermoelectric power cannot be added to the probeless measurements.