氮離子佈植於砷化鎵之特性研究

Abstract

我們將氮離子以160KeV的佈植能量及2x1015cm-2的佈植劑量於室溫下植入GaAs基板，500℃、700℃退火樣品是利用高溫爐管退火30分鐘，950℃的樣品則以RTA的方式退火30秒。由SlMS得知樣品中的氮在950℃的高溫退火下仍無明顯的擴散。而X-ray量測的結果告訴我們樣品晶格回復需經過500℃以上的退火處理。另外，我們也對N+離子佈植樣品進行一系列的電性量測。經由這些量測得知未退火樣品具備variable range hopping之載子傳輸特性，而500℃以上退火樣品則呈現高電阻特性。我們利用電流-電壓、導納頻譜、DLTS研究此高電阻材料後發現其符合SCL(space charge limited)半絕緣材料電流傳輸模型，並得到材料電阻造成的活化能有隨著退火溫度的上升而變大的趨勢，其中由導納頻譜量測所得材料電阻造成的活化能分別為0．20eV(as-implant)0.34eV(500℃退火)、0.59eV(700℃退火)、0.71eV(950℃退火)。

LEC(Liquid Encapsulated Czochralski) and semi-insulating GaAs(1OO) wafers are implanted at the room temperature with 160 keV N+ to a fluence of 2xl015cm-2. Rapid thermal annealing is performed at 950℃ for 30 seconds while furnace annealing is used below 700℃ for 30 minutes. After annealing at as high as 950℃, N shows no measurable redistribution by secondary ion mass spectrometry. From X-ray diffraction, it is found that the annealing temperature up to 500℃ is necessary for the crystalline regrowth. Electrical characteristics of the material are investigated in details. From temperature-dependent conductance measurement, the carrier transport for as- implanted sample is identified to be variable-range hopping. The samples annealed above 500℃ become highly resistive. By current-voltage, admittance spectroscopy, and deep level transient spectroscopy measurements, it is found that the high-resistive material shows the characteristic of a space-charge-limited current conduction governed by traps. The activation energy of the material resistance is found to increase with increasing annealing temperature. Admittance spectroscopy displays that the activation energy of material resistance for as-implanted sample is 0.20eV which increases to 0.34, 0.59, and to 0.71eV after annealing at 500℃, 700℃, and 950℃, respectively.