The Structural and Morphology of a Porous Inp

THE STRUCTURAL AND MORPHOLOGY OF A POROUS INP

Y.A. Suchikova1

1BSPU, Berdyansk, Ukraine

Annotation

The structural and morphology of a porous InP have been studied. The samples of porous InP were fabricated by an electrochemical method on n- type InP(100) in solution of 5 % HCl. The composition of the films was checked by energy dispersive X-ray analysis (EDAX). The pore sizeof porous InP wereestimated by scanning electron microscope.

Introduction

The last some years attention of researchers involve alongside with porous Si and other porous semiconductors, in particular compounds А3В5. The scope of porous compounds А3В5 constantly extends.

Porous substrates on the basis of compounds А3В5are perspective material for obtained homo- and hetero-epitaxial layersof high structural quality. Therefore obtained of high-quality porous structures is the important physical and technological problem that became an object of research of many scientists [1 – 3].

Experimental

Samples porous InP were prepareted by electrochemical etching of n-type (100) oriented crystalline InP substrate (concentration of impurities 2,3х1018cm-3). MonocrystalsInP have been made in laboratory of the company «Molecular Technology GmbH » (Berlin). As electrolytethe solution of 5 % HCl was used. As the cathode the plate of platinum served in an electrochemical cell. All experiment were carried out at room temperature in darkness. Before experiment samples were cleared in toluene and then were washed out in the distilled water. The voltage raised in due course with a speed 1V/min before detection of size of a threshold voltage in porous creation which in this case has made 3,5V (t=3min). After that the mode of the fixed voltage at which samples were etching during 2min. General time of etching 5min. After experiment samples were cleared by ethanol and dried in a stream of nitrogen during 10min. The morphology of the received porous structures was investigated by means of scanning electronic microscope JSM-6490. The сhemical compound has been studied by means of method EDAX. The structure of porous InP samples was investigated by X- ray diffraction with a DRON-3M difractometer.

Results and discussion

Detection of value of a threshold voltage in pores creation.

The voltage of the beginning of porous creation was defined as follows. Speed of change of a voltage made 1V/min (in during anodization). Thus the density of a current (up to critical value of a voltage) remained within the limits of 20 mА/cm2. Since Uс=3,5V the density of a current quickly accrued in due course – up to 250mА/cm2 within 1 minute (fig.1). It is possible to explain because of sharp increase of density of a current gradual increase in number of entrance apertures of pores and their branching under a surface.

Fig 1.Сurrent - voltage сharacteristic of porous InP during anodization.

After 1min. the current ceased to accrue (fig.2). Thus, the threshold voltage of the beginning of porous creation for (100) InP n-type with concentration of impurity 2,3х1018cm.-3 has made 3,5V.

It is necessary to note, that the threshold voltage of the beginning of pores creation depends from of some factors: concentration of impurities and orientations of the semiconductor, composition and temperatures of electrolyte, concentration of defects on a surface of a crystal, etc. Therefore this size has various values for each separately taken case.

Fig 2. Change of density of a current in time during electrolytic etchings.

Fig.3 shows the image of morphology of the porous sample of InP, received by electrolytic etchings n-InP (100) in a solution of a hydrochloric acid.

Fig.3. SEM image of surface n-InP(100) after pore formation in 5% HCl.

In figure it is possible to see the ordered ensemble of pores which was formed on a substrate from monocrystal of InP. Porous appeared on all surface of an ingot. The size of pores averages 40nm, that testifies that the given structure is nanosized. The size of the walls between pores is within the limits of 5-10nm. The similar result is technologically important as quality porous films is defined by the sizes nanostructure, a degree of porosity and uniformity of distribution of pores on a surface of the sample. The less size of pores and the more percent of porosity there is less, the more qualitatively porous structure is. Depth of germination of channels of pores makes approximately 35μm. It is necessary to note, that depth of a porous layer is also important characteristic. Degree of porosity makes approximately 30 % .

It is known, that process of etching occurs to various speeds on different surfaces. So, for n-InP with orientation of a surface (111) poles of etching have the triangular form (or very close this form). Investigated porous structures have been received on monocrystalInP with orientation of a surface (100). For such orientation formation of pores which have the form reminding in the section a square is characteristic.

Conclusions

Thus, as a result of the electrolitic etchings of crystals n-InP (100) in a solution of a hydrochloric acid India with the size of pores 40nm, distance between pores 5-10nm was possible to receive nanoporous layers of phosphide. Thus thickness of a porous layer has made 35μm. It testifies that as a result of annodization thin long channels of pores were formed parallel each other which in cross-section have the form close to a correct quadrangle . Such form of pores is defined by orientation of a surface of the investigated sample.

References

[1]V. P. UlinS. G. Konnikov, Semiconductors, 41 (2007) 832.

[2] S. Ben Khalifa , B. Gruzza, C. Robert-Goumetet. al., Surface Science, 601 (2007) 4531.

[3] S. Langa, J. Carstensen, I. M. Tiginyanuet. al., Electrochemical and Solid-State Letters, 4 (2001) G50.