Diffusion lengths of excited carriers in CdxZn1−xSe quantum wells

Abstract

Diffusion lengths of excited carriers in a Cd x Zn 1Ϫx Se multiple quantum well structure were determined for temperatures between room temperature and 8 K from cathodoluminescence measurements. The diffusion length was found to depend upon temperature and Cd concentration of the quantum well. For the highest Cd concentration (xϭ0.43), the diffusion length increased with temperature up to 225 K and then dropped at higher temperatures. Diffusion lengths were 0.21 m at 8 K, 0.38 m at 225 K, and 0.24 m at room temperature. For the well with least Cd concentration (xϭ0.24), longer diffusion lengths were obtained. The nature of the diffusing carriers is also discussed.

Imaging ambipolar diffusion of photocarriers in GaAs thin films

“…After the initial work on electrostatic coupling between electrons and holes 1 , significant theoretical and experimental work has been published on ambipolar diffusion in bulk materials 2,3 as well as in heterostructures 4,5 . The majority of recent studies consider undoped material so that the ambipolar diffusion constant is only related to hole diffusion [6][7][8] or to excitonic transport 9 . The dependence of the ambipolar diffusion constant, D a = (D n σ p + D p σ n )/(σ p + σ n ), on the unipolar diffusion constant D n (D p ) of electrons (holes) and of their partial conductivities σ n (σ p ) has never been detailed experimentally.…”

Diffusion lengths of carriers in n- and p-type ZnMgSSe cladding layers of green laser diodes

“…7 The Hall mobility of electrons at room temperature in n-type ZnMgSSe is typically between 100 and 300 cm 2 /V s, depending on dopant level and exact quaternary composition, 21,22 and that of holes is around 80 cm 2 /V s. 23 The holes are presumably the slower diffusing species, limiting the QW luminescence. The values that are found for L n and L p are therefore determined by the transport of the holes.…”

“…We have in the past used a modification of the method first reported by Zarem et al 10 to measure the carrier diffusion length in ZnCdSe quantum wells by means of cathodoluminescence ͑CL͒ microscopy. 7 This method involves deposition of opaque and transparent Au films. We are currently exploring how to use CL to determine carrier diffusion lengths in thicker semiconductor layers in actual laser devices.…”

“…Carrier diffusion lengths for bulk or thin-film ZnSe and CdSe have been determined by various groups and methods, [1][2][3][4][5][6][7] but the values of diffusion lengths of carriers in ZnMgSSe, employed as cladding material in II-VI based blue-green laser diodes, 8,9 has to the best of our knowledge not yet been reported. We have in the past used a modification of the method first reported by Zarem et al 10 to measure the carrier diffusion length in ZnCdSe quantum wells by means of cathodoluminescence ͑CL͒ microscopy.…”

Carrier transport properties in the vicinity of single self-assembled quantum dots determined by low-voltage cathodoluminescence imaging

“…The L a value increases from 120 to 390 nm between 300 and 120 K and then decreases down to 140 nm at 5 K. The carrier mobility also peaks around 100 K in III-V semiconductor quantum wells. 19,20 Moreover, the carrier lifetime in a thin quantum well is expected to be nearly constant at low temperatures ͑T Ͻ 120 K͒ and to decrease at higher temperatures due to thermal activation of the carriers and recombination into the InP barrier. We thus obtain a fair qualitative agreement with the expected L a ͑T͒ function.…”