The hall mobility and its relationship with persistent photoconductivity of undoped GaN

Abstract

Special Issue PaperHall effect measurements have been widely used to characterize electrical properties of undoped and doped GaN. 1,2 The Hall mobility is indicative of electrical quality of undoped GaN in optimization of growth conditions. 3,4 Although a number of models have been proposed to explain anomalous behavior of the Hall mobility dependency on the electron density, 5-7 mechanism, which dominates the Hall mobility of undoped GaN, still remains unclear. The yellow-band luminescence (YL) and persistent photoconductivity (PPC) have also been observed and extensively investigated in undoped and doped GaN. 8,9 A recent report claimed that PPC and YL in GaN are related to each other through defects associated with a broad deep level. 10 The origins of YL and PPC are still in debate. [8][9][10][11] In this work, a variety of undoped GaN with electron densities on the order of mid-10 16 cm -3 and with a Hall mobility varying from < 50 cm 2 /sV to > 500 cm 2 /sV at room temperature were investigated using temperature variable Hall effect measurements. The objective was to better understand what limits the Hall mobility of undoped GaN as well as its relationship with the PPC effect.Undoped GaN samples were grown on (0001) orienTemperature-variable Hall effect measurements have been used to investigate the electrical properties of undoped GaN, which have the electron densities on the order of mid-10 16 cm -3 and a Hall mobility varying from < 50 cm 2 /sV to > 500 cm 2 /sV. We found that very strong ionized impurity scattering limits the Hall mobility of GaN. Illumination even at 77 K has very little effect on the electron density but can lead to a noticeable persistent increase of the Hall mobility. The induced persistent photoconductivity (PPC) effect is therefore related to the Hall mobility through intrinsic electrically active defects. The properties of those defects were further investigated by monitoring a transient change of resistivity after removal of illumination at different temperatures. It reveals that the recapturing process of excited electrons into illumination-neutralized defects is the mechanism responsible for the PPC effect of undoped GaN.Key words: Undoped GaN, Hall effect, persistent photoconductivity, Hall mobility tated sapphire by metal organic vapor phase epitaxy (MOVPE). Trimethylgallium (TMGa) and NH 3 were used as the precursors. The carrier gas was H 2 . Growth conditions for undoped 3 µm thick GaN were fixed, while growth parameters used for GaN buffer layers were widely changed to vary the doping concentration of the undoped GaN samples. Temperature-variable Hall effect measurements were carried out using a BIO-RAD Hall effect system over a temperature range of 90-500 K. The samples were in van der Pauw geometry using In dots as ohmic contacts. The samples were first measured at room temperature and then heated up to 500 K in the dark. Temperature-variable-Hall effect measurements were carried out from 500 K to 90 K in the dark. The Hall effect or simple resistivity measurements wer...

Solution-Grown ZnO Films toward Transparent and Smart Dual-Color Light-Emitting Diode

“…The electrons travel a short distance if they recombine along the outmost edge of the LED mesa; thus the edge emission can be still obvious (Figure g). However, as the electron mobility in n-GaN can be quite high (hundreds of cm 2 ·V –1 ·s –1 ), the radiative recombination is not limited to the edge of the LED mesa, as corroborated by the appearance of green light within the contour of the LED under reverse bias (Figure b). The nonhomogeneity of the emission across the LED mesa may be caused by the nonuniform distribution of recombination centers as well as nonuniform current spreading across the ZnO layer, which needs to be improved.…”

Self-consistent scattering analysis of Al0.2Ga0.8N/AlN/GaN/AlN heterostructures grown on 6H-SiC substrates using photo-Hall effect measurements

“…Mobility enhancement after illumination in semiconductor systems has been reported by several groups [25][26][27][28][29][30]. due to photoexcitation at a fixed temperature can be attributed to the increased electron mean energy with the increasing carrier density in the 2DEG channel, which results in a less efficient interaction of the 2DEG electrons with the ionized donor impurities as well as improved screening [25,27].…”

The role of the grain boundary on persistent photoconductivity in GaN

“…The nature of several defects and their effects on the optical and transport properties of GaN are not well understood. For example, (i) an anomalously long relaxation time of photoexcited carriers is commonly observed in GaN [3][4][5][6][7][8][9][10], but so far the microscopic origin of this phenomenon is not understood; (ii) extended defects, like a grain boundary or dislocation, are commonly observed in GaN [2],…”

“…A columnar structure is often observed in transmission electron micrographs [2]. Grain-boundary induced potential fluctuation has been used to explain the anomalous Hall results [10,[13][14][15] of the dependence of mobility on carrier concentration and anomalous conductivity results [16] in the ion-implanted epitaxial layer. Wang et al [10] have shown that Hall mobility in undoped GaN is related to the long relaxation time of photoexcited carriers due to the presence of a charged dislocation-point-defect complex.…”

“…In the microscopic random potential fluctuation (RPF) model [27], it has been proposed that random local potential fluctuations separate the photoexcited carriers and causes PPC. There are already several reports [3][4][5][6][7][8][9][10] on the observation of PPC in both n-type and p-type GaN. Most of the investigations on PPC in GaN are focused on the mechanism of decay kinetics.…”