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Kamalov Ikhtiyor Ramazonovich, Tashkent State Technical University, Ph. D., in Technical Sciences, Associate Professor Kanatbaev Sagidat Saduovich, Navoiy State Pedagogical Institute, faculty member E-mail: kamalova.di@mail.ru
TECHNIQUE OF INDIUM METAL-PHOSPHIDE CONTACTS PERFORMANCE ENHANCEMENT BY MEANS OF CHEMICAL TREATMENT
Abstract: It was established that chemical treatment affects stoichiometry of the indium metal-phosphide surface, thickness and phase composition of native oxides. To obtain indium metal-phosphide contacts (M-n-InP), having nearly ideal characteristics, before metal deposition, one shall treat M-n-InP surface in HF, HCl, H2SO4, H3 P04 acid solutions. In this case, one shall give a priority to H2SO4: H2 02: H2 O solutions, giving minimum contacts parameters spread within the plate area. The same result may be obtained with the parameters of the contacts Au-n-InP, formed on the indium phosphide surface after treatment in HCI: H2O and H3 PO: H2 O.
Keywords: metal, phosphide, indium, contact, semiconductor, oxide layer, dielectric, surface, density, layer thickness.
Studies of laminated multiphase structures are an important branch of chemistry, physics and semiconductor technique, being theoretical and technological fundament for development ofdiscrete devices and integrated circuits. Enhancement of finished products quality and reliability requires comprehensive approach, covering all stages of device manufacturing. The characteristics of indium metal-phosphide contacts (M-n-InP) depend on the surface physical and chemical properties, which are to a large extent determined by pretreatment processes, affecting a surface stoichiometry, thickness and phase composition of native oxides. As far as chemical treatment is considered as the method of affecting, having the most evident impact on a surface condition, therefore, correct selection of the modes of conduction gain significant importance for semiconductors developing and forming of Schottky barriers with reproducible parameters.
Treatment in the solutions based on non-organic acids gives indium phosphide surface with minimum thickness of native oxide. In this particular case, it consists in a proximity of the values of an ideality factor n k 1.7; oxide layer thickness dok = 0.5 ^ 0.7 nm and small difference of potential barrier values F^f, found based on lin-
ear reverse current-voltage (CVC) and current-capacity (CCC) characteristics. At the same time, alkaline solutions H2O2: H2O and Br2: CH2 COOH leave on the treated surface quite thick native indium phosphide oxide (InP) dok = 1 * 2.5 nm.
The contacts Au-n-InP, formed on the indium phosphide surface after such treatment, have the ideality factor (n) much exceeding 1.0. It follows, that when we want to obtain the contacts M-n-InP having nearly ideal characteristics, then one shall treat indium metal-phosphide surface in HF, HCl, H2SO4, H3 PO4 acid solutions before metal deposition.
In this case one shall give a priority to H2SO4: H2 O2: H2 O solutions, giving minimum contacts parameters spread within the plate area.
The contacts Au-n-InP, formed on the indium metal-phosphide surface after treatment in HCI: H2O and H3 PO: H2 O, have also small parameters spread, when n is approximate to 1.0. But as opposed to H2SO4: H2 O2: H2 O, after treatment in HCl: H2 O and H3 PO4: H2 O we note much sharper drop of intensity of the edge photoluminescence of the chemically processed indium phosphide when it is subsequently treated at
Section 8. Technical sciences
T , = 353 - 523 K (Table 1). It is natural, that this can
anneal v 7 '
lead to increased parameters sensibility of the contacts M-n-InP, formed on the surface treated with HCl: H2O u H3 P04: H2 O as compared to the treatment in H2SO4: H2 O2: H2, to the manufacturing temperature conditions.
As to the parameters spread of the contacts Au-n-InP within the plate area in the process of InP treatment in other solutions: Br2: CH3COOH, HF: H2 O, in our opinion, the main reason is the variation of native oxide layer
Table 1. - The effect of indium phosphide surface
thickness (NO) and of the interface phase composition, determining surface state energy structure. This conclusion is based on the observed discrepancy between the values n and Fe of the contacts, formed in different points of a surface, when increase of the value n is not always followed by increase of Fe, and vice versa, the contacts with the maximum value Fe not always have very high values of n.
treatment on edge photoluminescence intensity
No. Solution composition Edge photoluminescence intensity, relative units
°«g. T.nn..l = 353 0K 430 0 K 523 0 K
1. Br2: CH3: COOH 0.1 2.7 3.3 1.5
2. KOH: H2O2 48 0.2 0.1 0.2
3. NH4OH: H2O2 6.3 0.18 0.1 0.13
4. H.SO^ H2O2. H:O 23 17 10 14
5. HF: H2O 79 12 12 31
6. HI: H2O 105 11 19 46
7. HCl: H2O 79 13 11 8.6
8. H:O2, H2O 2.8 0.3 0.23 0.17
9. H3PO4 H2O 79 1.9 0.67 0.82
It should be recognized, that NO availability on indium phosphide surface is not always negative. When we analyze the effect of chemical treatment on U, ,
' break
(breaking voltage), we can see that Schottky barriers with minimum NO thickness have also minimum U, ,. At the
break
same time NO formation between a metal and a semiconductor after InP surface treatment in such solutions as Br2: CH3COOH, NH2OH: H2O, H2 O2: H2 O ensures significant increase of U, ,. The absence of such effect
C» break
when indium metal-phosphide surface is treated in KOH: H2, which also results in formation of NO with a significant thickness, can be explained by the distinguishing features of the formed NO phase composition.
While analyzing electrical characteristics of the contacts Au-n-InP, one shall note the fact, that Schottky barriers, formed on the surface treated in alkaline medium (pH > 7), have lower temperature dependency Is, which demonstrates reduced Fb of such contacts. In fact, after treatment in acid solutions (pH > 5), the value Fb of the contacts Au-n-InP, determined based on the dependency Inl/T2 = f (1/T), amounts 0.34-0.44 eV, but after treatment in alkaline solution KOH: H2 O the value Fb of the contacts amount 0.2-0.3 eV. Remember, that the value Fb in the indium metal-phosphide system is
determined by defects energy structure, therefore this situation can be considered as one more evidence for the conclusion, that chemical treatment by means of selection of an appropriate etching agent composition, allows not only to control NO phase composition, but also at a large extent to control energy structure of the defects, affecting the value Fb. We can estimate the real processed based both on the change of edge photoluminescence intensity, which is quite sensitive, and on the rate of surface recombination, determined by surface conditions density and energy position. As one can see from the (Table 1), the values obtained after treatment in alkaline medium, especially with subsequent thermal processing at T , = 353 ° K, are quite lower, than after InP
O anneal 'A '
treatment in acid solution.
When we consider the model of surface conditions with continuous energy distribution (Ns), then this change Ns after treatment with alkali is consistent with the observed displacement of Fermi level of the surface within a single conduction band. We can also estimate Ns increase at the energy >1/2InP based on measurements of Ns (Eg) - Fermi level energy of a surface, using CCC of the structures with thin metal dielectric-semiconductor (TMDS) of the structures Al-n-InP, where in-
dium phosphide surface has been treated in NH4OH solution before AI2O3 deposition [1].
Note, that the conclusion about the possibility to control physical and chemical properties of a surface, and, consequently, indium metal-phosphide interface parameters, absolutely complies with the modern vision
of the processes, occurring at the solid-liquid interface and is in direct correlation with the effect of a solution pH on reductive-oxidative properties of the surface group of atoms and on NO concentration of induced conditions [2].
References:
1. Газаков О., Чарыев Я., Оразбердиев А. «Некоторые электрические свойства диодных структур на основе Au-InP». Изв. АН ТССР Сер. ФТХ и Г., - 1985.
2. Бахадирханов М. К., Ибрагимов Ш. Б., Камалов И. Р. «Влияние химической обработки на поверхностные состояния и электрофизические характеристики Au - n - InP структур». Электронная обработка материалов. Кишинев, - 2004. - № 2. - С. 92-95.
