Magnetoresistance in low-temperature grown molecular-beam epitaxial GaAs

Abstract

Reduction of variable range hopping conduction in low-temperature molecular-beam epitaxy GaAsHeavily carbon-doped In 0.53 Ga 0.47 As on InP (001) substrate grown by solid source molecular beam epitaxy Conductivity, Hall effect as well as ''physical'' and ''geometrical'' magnetoresistances were measured at 290-440 K in molecular-beam epitaxial GaAs layers grown at 200-400°C. The experimental data were analyzed taking into account the combined band and hopping conductance regime. Positive hopping magnetoresistance parameters (⌬/ 0 B 2 ) h Ϸ10 Ϫ4 T Ϫ2 and hopping Hall mobilities lower than 1ϫ10 Ϫ4 m 2 V Ϫ1 s Ϫ1 were determined in the as-grown layers. A transverse-to-longitudinal hopping magnetoresistance ratio of about 2, consistent with hopping transport theories, was obtained. In the annealed layer grown at 200°C ͑J200a͒ the band mobility determined from the geometrical magnetoresitance ͑GMR͒ mobility was found to be significantly higher than the band Hall mobility. It is related to a mixed band conductivity regime with the hole concentration p exceeding the electron one n. The difference between GMR and Hall mobilities decreases with increasing growth temperature as far as a typical single-carrier band conductivity regime (nϾ p) is present in the layer grown at 400°C. In contradiction to the layers grown at higher temperatures, the J200a layer showed the opposite ͑positive͒ sign of the hopping Hall coefficient as well as the largest hopping magnetoresistance parameter (Ϸ3ϫ10 Ϫ2 T Ϫ2 ).

Ultrafast Phenomena in Freestanding LT-GaAs Devices

“…• C with a growth rate of about 1 µm/h [3,6]. After the MBE deposition, wafers with LT-GaAs layers were annealed in situ at 600…”

“…These properties make LT-GaAs the material of choice for fast and sensitive photodetectors [4][5][6][7][8][9][10][11][12][13][14] and photomixers [15][16][17][18][19][20]. Typically, LT-GaAs films are grown by molecular beam epitaxy in the temperature range from 200…”

“…• C [3,6]. Artificially created deep-level traps are responsible for the very short carrier lifetime in LT-GaAs based opto--electronic devices.…”

Indication of Mixed Conductivity in III-V Semiconductors Using Conductivity, Hall Effect and Magnetoresistance Measurements

“…It is more convenient to determine the parameter S PMR as the slope of a 1/B 2 versus R 0 /DR plot [6]. This treatment is applicable also for S GMR if the 1/B 2 versus R 0 /DR plot is linear (it occurs if (R H0 s 0 ) 2 ( S PMR ) [9]. From the above equations it follows…”

“…[6] and Fe-doped InP [7,8]. The necessity to investigate this phenomenon has arisen recently in connection with low-temperature-grown molecularbeam epitaxial GaAs layers [9], as well as with irradiated GaAs layers [10].…”