Protective capping and surface passivation of III-V nanowires by atomic layer deposition

Joona-Pekko Kakko,Esko Kauppinen,Naeem Shahid,Hua Jiang,Veer Dhaka,Shagufta Naureen,Harri Lipsanen,Alexander Perros,Anand Srinivasan,Tuomas Haggren

doi:10.1063/1.4941063

Joona-Pekko Kakko, Esko Kauppinen + Show 8 more

Open Access

https://doi.org/10.1063/1.4941063

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Abstract

Low temperature (∼200 °C) grown atomic layer deposition (ALD) films of AlN, TiN, Al2O3, GaN, and TiO2 were tested for protective capping and surface passivation of bottom-up grown III-V (GaAs and InP) nanowires (NWs), and top-down fabricated InP nanopillars. For as-grown GaAs NWs, only the AlN material passivated the GaAs surface as measured by photoluminescence (PL) at low temperatures (15K), and the best passivation was achieved with a few monolayer thick (2Å) film. For InP NWs, the best passivation (∼2x enhancement in room-temperature PL) was achieved with a capping of 2nm thick Al2O3. All other ALD capping layers resulted in a de-passivation effect and possible damage to the InP surface. Top-down fabricated InP nanopillars show similar passivation effects as InP NWs. In particular, capping with a 2 nm thick Al2O3 layer increased the carrier decay time from 251 ps (as-etched nanopillars) to about 525 ps. Tests after six months ageing reveal that the capped nanostructures retain their optical properties. Overall, capping of GaAs and InP NWs with high-k dielectrics AlN and Al2O3 provides moderate surface passivation as well as long term protection from oxidation and environmental attack.

Highlights

Semiconductor nanowires (NWs) are being actively pursued as building blocks for generation nanotechnology enabled systems
We suspect that the as-grown GaAs NWs, owing to their small diameters (∼40 nm), are likely to be totally depleted of free carriers with the depletion length extending throughout the NW volume due to the strong Fermi level pinning.[1]
To address the issue of surface passivation, and further prevention from the long term oxidation of the surface, we studied their optical properties after capping the surface with various atomic layer deposition (ALD) grown films of AlN, TiN, Al2O3, GaN. and TiO2, respectively

Summary

INTRODUCTION

Semiconductor nanowires (NWs) are being actively pursued as building blocks for generation nanotechnology enabled systems. There exists few previous reports where atomic layer deposition (ALD) grown AlN films were used as gate dielectric layers for the surface passivation of thin film based GaAs materials[10,11,12,13] but hardly any systematic report exists studying the effect of different dielectric layers on the surface of III-V NWs and their optical properties. We have investigated a wide range of ALD grown materials (AlN, TiN, Al2O3, GaN, and TiO2) as capping and surface passivating layers for GaAs and InP nanowires and nanopillars. GaAs, another additional property both these materials possess is the self-cleaning of the GaAs NW surface (thinning of native oxide after the deposition).[12,16,17] In this study, we have used the photoluminescence (PL) and time-resolved photoluminescence (TRPL) techniques to study the optical properties of III-V NWs after capping them with a wide range of ALD grown materials. The aim was to evaluate if these ALD materials provide some degree of passivation and protection from long term oxidation without having any adverse effect on the NW surface

EXPERIMENT

RESULTS AND DISCUSSION

CONCLUSION