High-breakdown-voltage AlSbAs/InAs n-channel field-effecttransistors

InAs channel field-effect transistors of 1-μm gate length were grown by molecular beam epitaxy and observed to operate at channel electric fields (20 kV/cm) higher than previously demonstrated and several times greater than the threshold for impact ionization in bulk InAs. Voltage gains on the order of 10 were observed with transconductances as high as 414 mS/mm and output conductances as low as 33 mS/mm. These voltage gains are comparable to those of GaAs-based devices and are the highest observed for InAs channel devices. The results demonstrate the potential for practical room-temperature operation of InAs FETs     

p-channel modulation-doped field-effect transistors based on AlSb0.9As0.1/GaSb

Operation of the first AlSbAs/GaSb p-channel modulation-doped field-effect transistor (MODFET) is reported. Devices with 1-μm gate length exhibit transconductance of 30 and 110 mS/mm at room temperature and 80 K, with respective maximum drain current densities of 25 and 80 mA/mm. The low field Hall mobility and sheet carrier density of this modulation doped structure were 260 cm²/V-s and 1.8×10 ¹² cm^-2 at room temperature and 1700 cm²/V-s and 1.4×10¹² cm^-2 at 77 K. Calculations based on these results indicate that room-temperature transconductances of 200 mS/mm or greater could be achieved. This device can be integrated with an InAs n-channel HFET for complementary circuit applications     

Feed bunk length requirements for Holstein dairy heifers

The objectives of this study were to determine the necessary feed bunk length per heifer and to assess the feeding behavior of heifers fed from bunks of varying sizes. Heifers in three age categories were used for three 16-wk experiments. In Experiment 1, feed bunk lengths per heifer were 15 or 31 cm, and, in Experiments 2 and 3, the lengths were 15, 31, or 47 cm per heifer. Heifers were fed a total mixed ration at restricted intakes. Within-group growth analyses showed uniform growth rates for all heifers at all feed bunk lengths. Individual heifer growth within each group did not vary significantly for either length used in Experiment 1. In Experiment 2, heifers fed from a 15-cm bunk had more variation in live weight gain than did heifers fed from 31- or 47-cm bunks. Live weight gains of heifers fed from a 31-cm bunk varied more than those of heifers fed from 15- and 47-cm bunks in Experiment 3. The mean number of eating bouts and meals and the mean meal duration showed differences between the 15-cm feed bunk length and the 31- and 47-cm feed bunk lengths in Experiments 1 and 2. In Experiment 3, this behavior was different across all lengths. Based on growth responses and feeding behavior, heifers that grow rapidly and that are fed a high quality total mixed diet in a free stall or a bedded pack group housing system require 15-, 31-, and 47-cm feed bunk lengths at 4 to 8, 11.5 to 15.5, and 17 to 21 mo of age, respectively.     

A complementary heterostructure field effect transistor technologybased on InAs/AlSb/GaSb

A complementary heterojunction field effect transistor technology based on the InAs/AlSb/GaSb system is proposed. The structure is formed by the vertical integration of InAs n-channel and GaSb p-channel HFET devices. The superior transport properties of electrons in InAs and holes in GaSb and their band offsets to AlSb or AlSbAs yield devices with transconductances much greater than AlGaAs/GaAs n- and p-channel HFETs. It is shown that a complementary circuit fabricated from these devices could provide room-temperature performance up to six times greater than that predicted for AlGaAs/GaAs complementary circuits     

Resonant interband tunneling device with multiple negativedifferential resistance regions

The first observations of multiple negative differential resistance (NDR) regions in resonant interband tunneling devices are reported. In vertically integrated poly-type heterostructures of InAs/AlSb/GaSb, the peak voltages are reduced by a factor of 2 compared to the AlInAs/GaInAs material system, while high peak-to-valley ratios of 4:1 (17:1) at 300 K (77 K) are maintained. The InAs/AlSb/GaSb material system offers advantages for circuit applications of such devices, particularly operation at lower voltages     

Kink-free AlInAs/GaInAs/InP HEMTs grown by molecular beam epitaxy

Kink-free AlInAs/GaInAs/InP HEMTs have been fabricated from an MBE structure grown under normal growth condition. Devices with 1 mu m gate-length exhibit an extrinsic transconductance of 450 mS/mm and a maximum drain current of 600 mA/mm which represent the best results for 1 mu m gate devices. The DC output conductance shows no kink over the entire gate bias range. The elimination of the kink is attributed to the high quality AlInAs buffer layer and a low mismatch between the AlInAs buffer layer and InP substrate.<>     

AlGaAs-GaAs-InGaAs strained layer laser structure with performance independent of AlGaAs layer quality

An AlGaAs-GaAs-InGaAs strained layer laser structure has been shown to have a low threshold current density which is independent of AlGaAs layer quality. This threshold invariance is attributed to the use of a large GaAs region outside the InGaAs well to reduce the effects of traps in the AlGaAs on the active region of the laser and was demonstrated by characterising identical structures grown by molecular beam epitaxy (MBE) under different AlGaAs growth conditions. These results should have strong implications for the reliability and manufacturability of such lasers and for the integration with electronic devices where low temperature growth is required.<>     

Preventing Sodium Poisoning of Photocatalytic TiO2 Films on Glass by Metal Doping

Titanium dioxide (TiO₂) has received much attention as a photocatalyst, specifically in applications that require a mechanically robust thin film. TiO₂ is particularly useful because it does not absorb visible light, making it well suited for coatings on glass. Photocatalytic activity of TiO₂ films is strongly dependent on the substrate and it has been well established that sodium diffusion from glass has a negative effect on this activity. While the prevention of sodium poisoning is possible through the use of a precoating, this requires an additional coating and/or calcination step. Other remedies, such as acid treatment of the glass surface, are also time consuming. Therefore, it is a more attractive option to negate the effects of sodium diffusion without a separate processing step. In this paper, we examined the effects of silver, cobalt, copper, gallium, molybdenum, and tantalum doping on the prevention of sodium poisoning of sol–gel TiO₂ films by comparing the photocatalytic activities on glass and SiO₂ precoated glass. While sodium poisoning degraded the photocatalytic activity of undoped TiO₂ films by 70%, it was only 10% for Mo- and Ta-doped TiO₂ films. Molybdenum was superior to other dopants in terms of photocatalytic activity, both in the presence of sodium and in a sodium-free environment.