FORMATION, MORPHOLOGIES, COMPOSITION AND OPTOELECTRONIC PROPERTIES Vitali Parkhutik Department of Materials Science, Technical University of Valencia OUTLINE: Introduction Basics of p-Si growth Morphology and structure Chemical Composition Optical properties Electrical properties

P-Si IS AN INTERESTING RESEARCH ISSUE Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

STRUCTURE AND BAND DIAGRAM Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

SET-UP FOR p-Si GROWTH 1 part of 48% HF + 1 part of ethanol Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

ALL THIS IS THE POROUS SILICON Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop. Pore width, nmType of pore  >50 Micro Meso Macro

Why p-Si is interesting? 1. Fundamental theoretical background 1.1. Physics of bulk semicon- ductors and nanocrystals 1.2. Electrochemistry of semi- conductors 1.3. Electrical transport in non- ordered materials 1.4. Optical properties of nano- clustered semiconductors 2. Laboratory training 2.4. Electrical properties of porous silicon (dc and ac conductivity) 3. Applications 3.2.Light-emitting devices 3.1. Stabilization of PS properties 3.3. Chemical sensors 3.4. Biological and medical monitoring 2.1. Formation of porous silicon layers 2.2. Chemical composition of porous silicon 2.3. Optical properties of porous silicon 1.5. Physics of non-lineal dynamic systems Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

Electrones or holes? Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

KINETICS OF Si POLARIZATION IN WATER-CONTAINING ELECTROLYTES P-Si growth Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

DETERMINATION OF POROSITY 1. Gravimetric method M 0 – Mass of Si sample before anodizing M 1 – Mass of Si sample after anodizing M 2 – Mass of Si sample after removal pSi layer Introduction Basics growth Morphology Composition Electrical Optical

POROSITY OF p-Si INCREASES WITH THE ANODIC CURRENT DENSITY Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

Current density alters the type of porosity J a =10 mA/cm 2 J a =30 mA/cm 2 Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

PORE RADIUS INCREASES WITH THE ANODIC CURRENT DENSITY 25% HF, 10(1), 80 (2) and 250 mA/cm2 (3) Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

OUDULATING MACRO-PORES ARE PRODUCED BY PERIODIC CHANGE OF CURENT DESNITY Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

DopingEtching rate Illumination during etching n + p + p or n p n Very high High Medium Low Very low No influence Illuminated Dark Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop. DOPING LEVEL INFLUENCES THE p-Si GROWTH RATE AND STRUCTURE

FACTORS INFLUENCING THE p-Si GROWTH: Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop. - anodic current density, - HF concentration, - Si doping level, - illumination

Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop. PORE DIRECTIONS ARE FOLLOWING THE CRYSTALLOGRAPHY OF Si WAFER

Highly ordered macro-p-Si Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

Nanowires of Si preserve the crystallinity of bulk Si Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

Size of Si clusters can be determined through fitting Raman scattering data Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

Chemical Composition of p-Si SiH x (x=1,2,3) Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop. SiO x

A.c. conductivity of p-Si Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

Reflection of light from p-Si Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

OPTICAL ABSORPTION IN p-Si Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

Photoluminescence of p-Si Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.

Confinement effects in Si clusters Introduction Basics growth Morphology Composition Electrical Prop. Optical Prop.