超平坦 GaAs 量子井戸の発光像 とスペクトル計測 Ji-Won Oh ， Masahiro Yoshita ， Hirotake Itoh ， Hidefumi Akiyama, Loren Pfeiffer A ， Ken West A Institute for solid state physics, University of Tokyo,and CREST, JST Bell Laboratories, Lucent Technologies, USA. A

Novel growth-interrupt annealing technique with a cleaved-edge overgrowth (CEO) method in MBE growth:Atomically flat (110) GaAs quantum well [1] M. Yoshita, H. Akiyama, L. N. Pfeiffer, K. W. West Jpn. J. Appl. Phys. 40, L (2001). Slight variation in Ga supply results in the formation of characteristic surface step-edge patterns such as 2- or 3-ML high- islands or 1-ML- deep pits [2] M. Yoshita, H. Akiyama, L. N. Pfeiffer, K. W. West, Appl. Phys. Lett. 81, (2002) Introduction 600 ℃ 10 min 5X5  m

[3] J. W. Oh, M. Yoshita, H. Akiyama, L. N. Pfeiffer, K. W. West, Appl. Phys. Lett. 82, ,2003. Applied Physics Letters 表紙論文 ! 2- or 3-ML high islands 1-ML-deep pits [110] [001] Characteristic Surface Forms on Atomically Flat Surface

Purpose of experiment Carrier diffusion on atomically flat (110) GaAs /GaAlAs QW and its dependences on temperature ( 4K-120K ) observed by point and uniform optical excitation by Ti-Sa laser (730nm)

Schematic Diagram for PL observation at various sample position & temperatures PL AlGaAs GaAs 10nm 6nm 6.8  m 29% AlGaAs Atomically Flat (110) ! Ti-Sa Temp 4K 10K 30K 45K 60K 90K 100K 120K

4K 10K 30K 45K 60K 80K 100K 120K mm Image of 1-ML Deep Pits

Image and PL spectra of 2-3 ML High Islands mm 4K 10K 30K 45K 60K 80K 100K 120K

Atomically Flat (110) Surface 4K 10K 30K 45K 60K 80K 100K 120K mm

Sliced PL Profiles from Atomically Flat Surface gets thinner

Measurement of Diffusion Length at various low temperature with point excitation PL 6.8  m FWHM:0.95  m Reflection image  m

4K 60K100K 30K  m Spot PL images at various low temperature PL Image : Beam Reflection

Diffusion on Atomically Flat surface Longer diffusion length By Hilmer et. al. Phys. Rev. B (1990) At 30K  ps  4000 in our data

Conclusion ・ Observation of unique surface forms on atomically flat (110) interface in GaAs/GaAlAs QW via microscopic PL imaging 1-ML-deep pits: dark triangular regions (higher energy regions: carriers flow outside) 2~3 ML-high islands :bright PL spots (lower energy regions: carriers flow inside) ・ Carrier diffusion length in low temp. by point excitation : efficient carrier migration over 1 mm scale even at 4K which increases with temp ・ Slenderizing PL image with growing temp: well explained by the measured

80  m [001] [110] 30.0 ML 30.X ML 29.X ML As Ga Characterizing top surface of Sample with AFM 3~4 mm

Fabrication of QW sample by cleaved-edge overgrowth GaAs QW (110) 1 First MBE growth Second MBE growth in situ cleavage (001) GaAs (001) substrate

By means of cleaved-edge overgrowth method with molecular beam epitaxy and growth interrupt annealing, we fabricated (110) GaAs quantum wells having atomically flat interfaces. We introduced characteristic 1-ML-deep pits and 2~3-ML- high islands on atomically flat interfaces by adding fractional monolayer of GaAs, which are characterized by atomic force microscope (AFM). In PL observation with uniform excitation, pits are reproduced as dark triangle images due to higher energy than surroundi- ngs and islands as bright PL spots due to lower energy. With increasing temperature, we observe changes in their shape and enhanced contrast, which is explained by enhanced carrier diffusion length due to significant reduction of interface-roughness scattering. Abstract

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