Voltage controlled terahertz transmission through GaN quantum wells

We report measurements of radiation transmission in the 0.220--0.325 THz frequency domain through GaN quantum wells grown on sapphire substrates at room and low temperatures. A significant enhancement of the transmitted beam intensity with the applied voltage on the devices under test is found. For a deeper understanding of the physical phenomena involved, these results are compared with a phenomenological theory of light transmission under electric bias relating the transmission enhancement to changes in the differential mobility of the two-dimensional electron gas

A new MBE CdTe photoconductor array detector for X-ray applications

A CdTe photoconductor array x-ray detector was grown using Molecular Beam Epitaxially (MBE) on a Si (100) substrate. The temporal response of the photoconductor arrays is as fast as 21 psec risetime and 38 psec Full Width Half Maximum (FWHM). Spatial and energy responses were obtained using x-rays from a rotating anode and synchrotron radiation source. The spatial resolution of the photoconductor was good enough to provide 75 {micro}m FWHM using a 50 {micro}m synchrotron x-ray beam. A substantial number of x-ray photons are absorbed effectively within the MBE CdTe layer as observed from the linear response up to 15 keV. These results demonstrate that MBE grown CdTe is a suitable choice of the detector materials to meet the requirements for x-ray detectors in particular for the new high brightness synchrotron sources

Electrical studies of single-barrier Hg_(1-x)Cd_x Te heterostructures

We report an experimental study of the electrical properties of single‐barrier Hg_(1−x)Cd_xTe heterostructures grown by molecular‐beam epitaxy. At high temperature, the measured current is interpreted to be the sum of thermionic and tunneling hole currents. This analysis is applied to data from each of three samples, yielding values of the HgTe–CdTe valence‐band discontinuity between 290±50 and 390±75 meV at 300 K. In all three samples, data taken over the range 190–300 K are consistent with a valence‐band offset which decreases at lower temperatures. Current–voltage curves are taken at 4.2 K, yielding a novel single‐barrier negative differential resistance (NDR) due to electron tunneling. Theoretical simulations indicate that ΔE_v must be <100 meV at 4.2 K to produce NDR