Characterization of Materials and Devices by Near-Field Scanning Optical Microscopy
- PDF / 1,323,693 Bytes
- 12 Pages / 414.72 x 648 pts Page_size
- 97 Downloads / 209 Views
the tip-to-sample separation are a small fraction of the wavelength. In this "near-field" regime, the spatial resolution is given approximately by the tip diameter yielding resolutions as high as - A/40, or ,-. 15nm for visible wavelengths [2]. High spatial and spectral resolution characterization of materials and devices is performed both by collecting emitted radiation in the near-field [4, 5, 6] and by exciting local photoconductivity in the semiconductor with radiation from the tip. [5, 7, 8, 9] Using wavelength tunable excitation sources, near-field optical beam induced current (NOBIC),[10, 11] or near-field photocurrent (NPC) measurements provide information on the compositional and electronic structure of the semiconductor samples. In this paper we examine the low-temperature near-field photoluminescence from partially ordered GaInP, examining the role of domains of 50 to 200nm in size in determining the optical properties of spatially indirect recombination. We find a correlation between the variations of the spatial dependence of the peak energy and intensity in the large domain samples, but not in the small. We also study near-field optical beam induced current spectroscopy on heterostructure samples and determine the effect of tip diameter and optical penetration depth on the photocurrent spatial resolution.
171 Mat. Res. Soc. Symp. Proc. Vol. 406 0 1996 Materials Research Society
2.0
Figure 1: Photoluminescence spectra for the samples used in this study. Only a single emission band is observed for the disordered sample #1, while both low-energy and high-energy band are observed for #'s 2 and 3. Note too the increasing red-shift for increasing ordering.
1.5
S1.0/ 1.0
/a #1 sample 0.5
sample #2 sample #3
0.0
1.70
1.80
1.90 2.00 2.10
2.20
Energy (eV)
LOW-TEMPERATURE NSOM OF PARTIALLY ORDERED GAINP Optical properties of ordered GaInP Spontaneous long-range ordering is observed in the ternary III-V alloy compound GalnP 2 as alternating Ga- then In-rich planes along the [1111 direction forming a CUPtB structure.[12, 13, 14] Simply stated, the ordering doubles the unit cell size versus the disordered alloy. folding the L point back to the F point, reducing the direct band-gap and lifting the valence band degeneracy.[13, 15, 16] The degree of ordering is parameterized by r/ : 0 > ij > 1. where the layer sequence is Gal+,Inl-,P 2 and Gal-,,h1+,P 2 along the [111] direction. The band-gap reduction (BGR.) and valence-band splitting (VBS) have been recently examined
by low-temperature far-field photoluminescence excitation spectroscopy (PLE), where botth the BGR and VBS can be studied simultaneously.[17] For the observed excitonic transitions. the data shows the maximum BGR to approach 490meV for perfect ordering, close to the theoretical prediction of Mader, et al.[18].
sample #
1
2
:3
substrate
60 -+ [111]A
6' -+ [1111B
6' -+ [111B]
840
750
690
0 -
.32 -200nrn
.51
