Chemical Cleaning of GaSb (1,0,0) Surfaces
Chemical Cleaning of GaSb (1,0,0) Surfaces
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DOI：
10.1149/1.2096946
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发表时间：
1989-05
影响因子：
3.9
通讯作者：
L. J. G. Zazo;M. Montojo;J. L. Castano;J. Piqueras
中科院分区：
文献类型：
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作者：
L. J. G. Zazo;M. Montojo;J. L. Castano;J. Piqueras
GaSb（1，0，0）表面经过化学钝化和真空热处理后得到了清洁。研究了由氧化剂和酸组成的四种不同的腐蚀溶液，用于溶解氧化物。在H2SO 4：H2 O2：H2O的情况下，表面变得非常粗糙，不均匀地覆盖有氧化物，并且不适于随后的外延生长。研究的其余三种蚀刻剂，HCl：H2 Q：NaK（酒石酸盐）、HF：HNO 3：CH 3COOH和Br：甲醇，留下覆盖有薄钝化层的相当光滑的表面，可能由纯Sb、Sb 20-和Ga 20-组成，在480 - 510 ℃的真空中加热样品，可以很容易地除去这些杂质。在外延生长或制备负电子亲和势（NEA）光电阴极的关键阶段之一是制备清洁和平坦的表面。在这两种情况下，必须小心防止污染物（主要是碳）的存在。在NEA光电阴极的情况下，表面上少量C的存在会迅速降低效率。在分子束外延生长中，如果一些残留的C保留在表面上，则不能将其去除，除非样品在相当高的温度下加热。对于砷化镓，温度远远超过同成分蒸发的极限是必要的，这种处理会导致表面的小面化。在过去，氩离子轰击和随后的退火用于清洁半导体表面。然而，损伤恢复所需的温度再次远远超过一致蒸发温度，并且该过程不适合于表面制备。目前，通常使用的替代工艺包括用防止C吸附的薄氧化物层钝化GaAs表面[参见例如参考文献102]。（1）]。该薄层可以通过稍后在真空条件下加热样品而容易地去除。样品的蚀刻通过典型的氧化-溶解化学机制发生。所形成的氧化物溶解在一些酸性或碱性水溶液中。停止化学反应后，样品表面仍然覆盖着一层薄的氧化层，由于其化学活性，防止了表面上可能的污染物（如C）的吸附或反应。不幸的是，GaSb比GaAs更具反应性，因此GaSb在氧化剂环境中快速氧化。此外，Sb氧化物在酸或碱的水溶液中相当不溶，当氧化-溶解机制负责蚀刻反应时，在蚀刻期间引起不均匀性。已经提出了一些络合剂的存在，使氧化的Sb在蚀刻过程中可溶（2）。在这项工作中，我们报告的结果与几种蚀刻解决方案。形态学，俄歇测量，和RHEED已被用来证明这些蚀刻剂的适用性。
GaSb (1, 0, 0) surfaces have been cleaned by chemical passivation and later heat-treatment in ultrahigh vacuum conditions. Four different etching solutions consisting of an oxidant and an acid for oxide dissolution have been studied. With the H2SO4: H202: H20 the surfaces become very rough, unevenly covered with oxides, and not suitable for later epitaxial growth. The remaining three etchants studied, HCl: H2Q: NaK (tartrate), HF: HNO3: CH3COOH, and Br: methanol, leave rather smooth surfaces covered with a thin passivating layer, probably consisting of pure Sb, Sb20~, and Ga20~, which can be easily removed by heating the samples in ultrahigh vacuum at temperatures between 480 and 510~One of the crucial stages in epitaxial growth or in the preparation of negative electron affinity (NEA) photocathodes is the preparation of clean and flat surfaces. In both cases the presence of contaminants, mainly carbon, must be carefully prevented. In the case of NEA photocathodes the presence of small amounts of C on the surface rapidly degrades the efficiency. In molecular beam epitaxial growth if some residual C remains on the surface, this cannot be removed unless the samples are heated at rather high temperatures. For GaAs, temperatures well over the limit of congruent evaporation are necessary and this treatment causes the faceting of the surface. In the past, argon ion bombardment and later annealing were used for cleaning the semiconductor surfaces. However, the temperature needed for damage recovery is well over the congruent evaporation temperature again and this process is not suitable for surface preparation. At present, an alternative process consisting of passivating the GaAs surface with a thin oxide layer which prevents C adsorption is commonly used [see for example Ref.(1)]. This thin layer can be easily removed by later heating the sample in ultrahigh vacuum conditions. The etching of the sample takes place via the typical oxidation-dissolution chemical mechanism. The formed oxide is dissolved in some aqueous acid or basic solution. After stopping the chemical reaction the sample surface remains covered with a thin oxide layer, that because of its chemical inactivity prevents the adsorption or reaction of possible contaminants like C on the surface. Unfortunately GaSb is more reactive than GaAs and thus GaSb is quickly oxidized in an oxidant ambient. Moreover, the Sb oxides are rather insoluble in aqueous acid or alkali solutions causing inhomogeneities during etching when the oxidation-dissolution mechanism is responsible for the etch reaction. The presence of some complexing agent that renders the oxidized Sb soluble during the etching has been proposed (2). In this work we report results obtained with several etching solutions. Morphology, Auger measurements, and RHEED have been used to demonstrate the suitability of some of these etchants.