Browsing by Author "Ngumbu, R.G.,"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Determination of Hall Effect Parameters of Gallium Arsenide and Gallium Manganese Arsenide by Van Der Pauw Geometry
    (2012) Kemei, S.K*; Kirui, M.S.K.,; Ndiritu, F.G.,; Odhiambo, P.M.,; Ngumbu, R.G.,; Amollo, T.A .
    Gallium Arsenide (GaAs) has been used widely in electronic industry to make diodes and transistors. As a semiconductor, it can be doped up with impurities with magnetic properties such as manganese to increase its electron conductivity. The storage capacity of the electronic devices made of gallium manganese arsenide (Ga1-xMnxAs) and the proportion of manganese atoms is worth studying. Here, GaAs was doped at different manganese levels, x, and the charge carrier concentrations at varied applied magnetic fields was investigated using Van der Pauw configuration. The tests were conducted at room temperature of 230C with magnetic field, 0.9 ≤ B ≤ 3.6mT and direct current of 1.19A. All the samples were studied for their hall voltage VH, carrier mobility µ, hall resistivity ρH and charge carrier concentration for different values of x. It was determined for Ga1-xMnxAs, 10% ≤ x ≤ 20% range, has maximum hall resistivity at B≈ 1.9 mT. For x=10%, 44.0 . ρ H ≈ Ω m ; x=20%, 79.0 . ρ H ≈ Ω m and for x=1%, the applied magnetic field has no effect on hall resistivity at initial states until B≈1.7mT. Beyond this point, magnetic field increases linearly with the hall resistivity to a maximum of 72.0 . ρ H ≈ Ω m . Maximum hall resistivity for x=50% was 2596.0 . ρ H ≈ Ω m at B mT ≈ 0.9 . For 0 20% ≤ ≤ x , carrier mobility µ , was of order of 7 2 1 1 10 m V s − − − while for x = 50% , µ was of order 9 2 1 1 10 m V s − − − . It was found out that the most probable doping percentage of GaAs with Mn dopants is approximately 20% and 10% as they show a hysteric response to an applied magnetic field. It suggests a good doping level of GaAs for making of volatile memory chips.
  • Thumbnail Image
    Item
    Determination of optical band gap and heat dissipation of Ga1-xMnxAs with Light in UV-VIS-IR Region using OSA SPECTRO 320”,
    (International Knowledge Sharing Platform, 2012) Kemei, S. K* .,; Kirui, M.S.K.,; Ndiritu, F.G.,; Ngumbu, R.G.,; Odhiambo, P.M.,; Amollo, T.A.
    Heat generated by silicon-based transistors due to high energy photo irradiation interferes with the electronic conductivity of transistors in the ICs. There is need to search for an alternative semiconductor material for making diodes and transistors with little or no heat dissipation. Dilute magnetic semiconductor such as Gallium Arsenide (GaAs) has demonstrated to be a better candidate to substitute silicon in electronic technology. UV-VIS-IR light was illuminated on the Ga1-xMnxAs samples of thickness 500nm−1000nm of varied doping levels during the study. Reflectance and transmittance spectra were determined using OSA SPECTRO 320 with light obtained from sodium lamp (240V, 100 W) with irradiance of 33.4807 W/m2 . The maximum absorbance within the UV-VIS-IR range was, A≤ 83.82% at λ≈200nm and minimum absorbance was, A≥0.96% at λ≈300nm with Ga1-xMnxAs, x=20% having the highest absorbance value and Ga1- xMnxAs, x=1%, the least absorbance. For Ga1-xMnxAs; x=0, x=10%, x=1% and x=20%; maximum absorbance occurred at UV region while for x=50%, maximum absorbance was observed at λ≈707nm. The results show that GaAs generate most heat due to its wide optical energy gap of 1.43eV while for x=1% dissipates little heat because of its small optical energy gap of 0.36eV.