Low Frequency Noise In n-Type Gallium Nitride
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"*** CRHEA, rue Bernard Gregory, F-06560 Valbonne, France. ABSTRACT Low frequency noise has been investigated in hexagonal n-type GaN with equilibrium electron concentration n - 1017 cm"3 at T=300 K. The frequency and temperature dependencies of the spectral density of the current noise, SI, have been studied in the frequency rangef from 20 Hz to 20 kHz. Over the whole temperature range from T= 80K to 400K the S1 ) dependence is very close to 1/f. The value of the Hooge constant, a , is very large: a - 5 - 7 and is found to be temperature independent. The effects of illumination on the low frequency noise in GaN are studied for the first time. The noise is unaffected by illumination with photon energy Eph < Eg, while band-to band illumination (Eph- Eg ) influences the low frequency noise, increasing the noise at higher temperatures, and decreasing it at lower temperatures. INTRODUCTION GaN has a very high potential for manufacturing of blue and violet photodiodes and lasers, UV detectors [1, 2], as well as for high power microwave electronics. Recently, the AlGaN-GaN HFET with a generation frequency higher than 70 GHz was reported [3]. The level of low frequency noise is one of the important parameters for photodetectors and microwave generators which determines the possibility of their applications. Also, it is well known that the level of low frequency noise reflects the structure quality of the material [4, 5]. Investigation of surface and contact noise can be used as a nondestructive method for quality control of devices [6, 7]. The investigation of low frequency noise in GaN is especially important because the structure quality of this material and the quality of contacts and surfaces is still insufficient, and need significant improvement. However, as far as we know, no investigations of low frequency noise in GaN were performed. In this work, the low frequency noise in n-type GaN with room temperature electron concentration n = 7 10 17 cm73 has been investigated. The results are compared with the data for Si and GaAs. EXPERIMENTAL DETAILS The samples of hexagonal polytype gallium nitride were grown by epytaxy on a sapphire substrate. The structure consisted of a 250 A buffer layer of GaN grown at 600 'C, of 0.8 gtm 21 Mat. Res. Soc. Symp. Proc. Vol. 512 ©1998 Materials Research Society
layer of GaN, and of a 200 A layer of AIN grown at 1080 *C. Over the AIN layer, a 1.0 gim GaN layer was grown at 1080 *C. The carrier concentration of the upper GaN layer at room temperature was n = 7 10 17 cm-3 . Ni-Au contacts were used. The sample had one pair of current and two pairs of potential contacts. The distance between current contacts was L = 2240 jm, the distance between potential contacts was - l = 140 gim. The value of Hall mobility at room temperature was jiH -~ 45 cm 2lVsec. With temperature decreasing gH increased and reached the value gH - 60 cm 2/Vsec at T- 100 K. The donor level energy, Ed, was estimated as Ed - 260 meV. The low value of Hall mobility and its weak temperature dependence show that the in
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