Non-Stationary Photoconductivity of GaN Nanocomposites in Artificial Opal Matrix
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NON-STATIONARY PHOTOCONDUCTIVITY OF GaN NANOCOMPOSITES IN ARTIFICIAL OPAL MATRIX M. Niehus1, S. Koynov1, R. Schwarz1, N.A. Feoktistov2, V.G. Golubev2, D.A. Kurdyukov2, and A.B. Pevtsov2 1 Physics Department, Instituto Superior Técnico, IST, P-1096 Lisboa, PORTUGAL Tel: +351-21-841 7775, e-mail: [email protected] 2 Ioffe Physico-Technical Institute, RAS, 194021 St. Petersburg, RUSSIA
Abstract It was recently proposed to use synthetic opals as a host matrix for obtaining 3D arrays of electronic nanodevices [1]. In the present work the opal matrices were infiltrated with GaN. We study electronic properties of opal-GaN, by means of transient photoconductivity (TPC) measurements using 5 ns laser pulses at wavelengths above (266 nm) and below (532 nm) the GaN bandgap (3.4 eV). A broad plateau is observed in the photocurrent decay covering several orders of magnitude. We compare the results with measurements in conventional GaN.
Introduction Artificial opal was recently proposed as matrix for obtaining 3D arrays of electronic nanodevices, which allow to produce a six orders of magnitude higher density of active elements when compared to planar technology [1]. A successful use would enable to reach a working area of the junctions per unit volume in group-III-nitride-based light emitting diodes (LEDs) as high as 10 m2/cm3 and to reduce the current density by 3-4 orders of magnitude as compared with conventional planar systems. A recent work demonstrated the ability to infiltrate GaN into the opal void sublattice, and the structural properties of the material was characterised by X-ray diffraction, Raman spectroscopy and atomic force microscopy [2]. Here, we study for the first time electronic properties of opal-GaN, by means of transient photoconductivity (TPC) measurements using laser pulses of 5 ns duration from a Nd:YAG system at wavelengths above (266 nm) and below (532 nm) the GaN bandgap of 3.4 eV. The time domain covered extends over 10 orders of magnitude. We compare the results with the power law decay observed in conventional GaN.
G11.26.1
-4
10 -5
2.59
10
~V
Current [A]
-6
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10
2.57 -7
~V
10 -8
2.45
ID(K77)
10
~V
-9
10
IPh(K77)
-10
10 -11
1
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X,Y 1µm/div Z 20 nm/div
Figure 1: AFM image of opal infiltrated with GaN, fill factor 60 %; the dashed line indicates the hexagonal structure.
10 -12
10
IPh(K103)
10
100 Voltage [V]
1000
Figure 2: I-V curves for K77 under dark (squares) and photo (circles) conditions, and for K103 (triangles) under illumination. All curves follow a power law with index about 2.5, a signature of space-charge limited currents: I ∝ U2 (Mott-Guerney equation [3]).
Sample preparation The host material is a single crystal of synthetic opal, consisting of close-packed amorphous silica (SiO2) spheres with diameters of approximately 220 nm. The voids between the spheres have diameters around 45-90 nm, and up to 26 % is accessible by guest materials. Macroscopically, the 1 mm thick samples are porous and fragile. To introduce GaN into the opal matri
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