Quantum dot micro-LEDs for the study of few-dot electroluminescence, fabricated by focussed ion beam

https://doi.org/10.1016/S1386-9477(01)00506-9Get rights and content

Abstract

We present first results from a micrometer sized micro-LED fabricated for the electroluminescence (EL) investigation of very few to one self-assembled quantum dot. Utilizing focussed ion beam (FIB) implantation we were able to fabricate a LED consisting of crossed p- and n-doped stripes of a few micrometer width. Confined between both stripes is a layer of quantum dots symmetrically embedded in a thin i-layer. We show that good quality quantum dots can be grown on FIB implemented regions and present first EL spectra which agree very well with PL measurements.

Introduction

Focused ion beam (FIB) implantation is a suitable technology for the fabrication of laterally structured semiconductor devices and—in particular—lateral doping patterns. We use FIB to fabricate novel optoelectronic devices, e.g. a very sensitive photo conducting detector for single photon detection [1]. Even a micro-LED-array could be fabricated easily. All these devices contain buried doping stripes, written by FIB.

In this paper we present a micro-LED made of crossed doping stripes for electroluminescence (EL) investigations on few quantum dots.

EL from an ensemble of dots always shows an inhomogenously broadened spectra. Although it is possible to get detailed information on the energetic position of electron and hole levels, EL measurements on single quantum dots should provide additional information, e.g. on many-body effects related to the number of occupied electron and hole levels. Due to the difficulties in contacting one single quantum dot, there are only a few reports on single quantum dot spectroscopy. Zrenner et al. obtained EL results from single dots by STM injection [2], and Itskevich et al. reported EL from individual dots that were embedded in a very small, cross-shaped pin-diode, that was fabricated by selective wet chemical etching [3].

Our approach to single dot spectroscopy is somewhat similar. We also embed our quantum dot layer in a pin-diode. However, we believe that using FIB technology for the fabrication of crossed doping stripes is less complicated than using photolithographical methods requiring underetching. Combining FIB technology and conventional photolithography allows us to define two narrow doped stripes (with p- and n-doping, respectively) where the top stripe is oriented perpendicular to the buried stripe. On top of the layer containing the p-doped stripe, but below the n-doped stripe, a layer of quantum dots can be grown. The dot layer is symmetrically embedded within an undoped layer of 50nm GaAs. The cross-section area of the two stripes forms a micro-pin-LED with few quantum dots in the active region. Our goal is to achieve contact to one single dot in this active region and to study EL from within the cross section.

Reducing the stripe widths to 1μm and assuming the strongly three-dimensional character of the space-charge potential of the crossed stripes, the number of dots close to its saddle point should be in the order of one.

In this paper we present first results on room temperature operation of our micro-LED including electrical characterization and first EL- and PL-spectra.

Section snippets

Experimental

The micro-LEDs are fabricated by first growing an intrinsic buffer layer on a epi-ready GaAs substrate in an MBE. In this layer we define narrow (of the order of some micrometers or less), highly p-conducting stripes by using FIB implantation. Be+ ions from a liquid metal ion source at an energy of 100keV are used. The implantation doses are in the range from 1013 to 1014cm−2.

After dopant implantation and vacuum transfer back to the MBE the remaining layers are grown by MBE, including the

Results

In order to test the dot growth on FIB implanted GaAs substrate, PL measurements were performed before processing the sample. PL signals were taken on both spots where no implantation and where implantation with different ion beam doses was performed. There is no dependence of the PL signal on the spot position for areas where no implantation was made, indicating homogenous dot growth over the wafer.

On spots where Be ions were implantated we found that with increasing implantation dose the

Outlook

In conclusion, we were able to show that the growth of good quality quantum dots is possible in regions where FIB implantation was performed with doses up to 1015cm−2. We presented first results from our micro-LED and we obtained some promising results already at room temperature. Although we are able to obtain dot spectra from our micro-LED, we have not achieved single-dot spectroscopy yet since still some 104 dots can be found in the cross section of 100μm2. However, reducing the stripe

References (3)

  • A. Zrenner

    J. Lumin.

    (2000)
There are more references available in the full text version of this article.

Cited by (13)

  • Role of microbial nanotechnology in energy devices

    2022, Handbook of Microbial Nanotechnology
  • In situ CBrCl<inf>3</inf> etching to control size and density of InAs/GaAs quantum dots

    2011, Journal of Crystal Growth
    Citation Excerpt :

    It is important to develop a simple and reliable growth technique for a material with a low density of QDs, which is required to study an individual QD without interference from neighboring QDs and to fabricate a single QD device. Some techniques have been reported to obtain a low density of QDs for fabrication of single QD devices [7–13]. Thermal annealing is one of the commonly used techniques to control the size and density of InAs dots.

View all citing articles on Scopus
View full text