Lee Kevin C
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
J Res Natl Inst Stand Technol. 1998 Mar-Apr;103(2):177-200. doi: 10.6028/jres.103.012. Epub 1998 Apr 1.
Careful testing over a period of 6 years of a number of GaAs/AlGaAs quantized Hall resistors (QHR) made with alloyed AuGe/Ni contacts, both with and without passivating silicon nitride coatings, has resulted in the identification of important mechanisms responsible for degradation in the performance of the devices as resistance standards. Covering the contacts with a film, such as a low-temperature silicon nitride, that is impervious to humidity and other contaminants in the atmosphere prevents the contacts from degrading. The devices coated with silicon nitride used in this study, however, showed the effects of a conducting path in parallel with the 2-dimensional electron gas (2-DEG) at temperatures above 1.1 K which interferes with their use as resistance standards. Several possible causes of this parallel conduction are evaluated. On the basis of this work, two methods are proposed for protecting QHR devices with alloyed AuGe/Ni contacts from degradation: the heterostructure can be left unpassivated, but the alloyed contacts can be completely covered with a very thick (> 3 μm) coating of gold; or the GaAs cap layer can be carefully etched away after alloying the contacts and prior to depositing a passivating silicon nitride coating over the entire sample. Of the two, the latter is more challenging to effect, but preferable because both the contacts and the heterostructure are protected from corrosion and oxidation.
在6年的时间里，对多个采用合金化AuGe/Ni接触、有或没有钝化氮化硅涂层的GaAs/AlGaAs量子霍尔电阻器（QHR）进行了仔细测试，结果确定了导致这些器件作为电阻标准性能下降的重要机制。用诸如低温氮化硅这样的对大气中的湿度和其他污染物具有不透性的薄膜覆盖接触点，可以防止接触点退化。然而，本研究中使用的涂覆有氮化硅的器件在温度高于1.1 K时显示出与二维电子气（2-DEG）并联的导电路径的影响，这干扰了它们作为电阻标准的使用。评估了这种并联传导的几种可能原因。基于这项工作，提出了两种保护具有合金化AuGe/Ni接触的QHR器件不退化的方法：异质结构可以不进行钝化，但合金化接触点可以用非常厚（> 3μm）的金涂层完全覆盖；或者在接触点合金化之后且在整个样品上沉积钝化氮化硅涂层之前，可以小心地蚀刻掉GaAs盖层。在这两种方法中，后者实施起来更具挑战性，但更可取，因为接触点和异质结构都受到保护，免受腐蚀和氧化。
