We extend our previous theoretical analysis of electronic and optical properties of p‐type quantum well structures based on the two heavy‐ and light‐hole system to include all the three valence bands. These theories are then used to clarify the origin of the normal incidence absorption and photocurrent at photon wavelengths of 2 ‐ 3 μm, which was observed in addition to the absorption around 8 μm by a recent experimental investigation with heavily doped p‐type GaAs/AlGaAs multi‐quantum well (MQW) structures. In the theoretical analysis, the Hartree and exchange‐correlation many‐body interactions are taken into account within one‐particle local density approximation, and it is shown that normal incidence absorption occurs in two wavelength regions over the transition energy range higher than barrier height for p‐type GaAs/AlGaAs superlattices with well doping of 2 × 1019 cm−3; one region has broad absorption peaks with coefficients of about 5000 cm−−1 around 8 μm, and the other has two rather sharp peaks at 2.7 μm and 3.4 μm with 1800 cm−−1 and 1300 cm−−1, respectively. The result indicates that the theory explains the experimental observation well, as the theoretical and experimental results are in close agreement in general absorption features.

RADAR(Radio Detection and Ranging) is an important system for surveillance and reconnaissance by detecting a reflected signal which obtains the range from the radar to the target, and the velocity of the target. The magnitude of the reflected signal varies due to the radar cross section of the target, characteristic of the transmission and reception antenna, distance between the radar and the target, and power and wavelength of the transmitted signal. Thus, the RCS is the important characteristic of the target to determine if the target can be observed by the RADAR system. It is based on the material and shape of the target. We have measured the reflection signal of a simple square-shaped (20 × 20 cm) target made of a new material, a gallium-based liquid metal alloy and compared that of well-known metals including copper, aluminum. The magnitude of reflected signal of the aluminum target was the largest and it was 2.4 times larger than that of the liquid metal target. We also investigated the effect of the shape by measuring reflectance of the F-22 3D model(~1/95 ratio) target covered with/without copper, aluminium, and liquid metal. The largest magnitude of the reflected signal measured from side-view with the copper-covered F-22 model was 2.6 times greater than that of liquid metal. The reflectance study of the liquid metal would be helpful for liquid metal-based frequency selective surface or metamaterials.

Plasmons have been investigated in highly doped GaAs/A!o,2Ga,&i multiple quantum well structures using the far-infrared techniques of dispersive Fourier transform spectroscopy and polarized oblique-incidence reflection spectroscopy. The plasma-effective masses were obtained from comparison with van der P u w measurePmen!s, znd found to be considerably enhznced O L ~ !hs/r bulk values. This enhancement has been compared with that obtained using non-parabolicity theory. Good agreement is obtained, but the results suggest that the theory slightly underestimates the effect.

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