摘要
研究了分子束外延生长条件对高铟组分InGaAs材料性能的影响,分析了生长温度、V/III比和As分子束形态对In0.74Ga0.26As材料光致发光和X射线衍射峰强度、本底载流子浓度和迁移率的影响。测试结果表明:适中的生长温度和V/III比可以提高材料晶格质量,减少非辐射复合,降低本底杂质浓度。As分子束为As2时In0.74Ga0.26As材料质量优于As4分子束。当生长温度为570 ℃,As分子束形态为As2,V/III比为18时,可以获得较高的光致发光和X射线衍射峰强度,室温和77 K下的本底载流子浓度分别达到6.3×1
短波红外InGaAs探测器具有高灵敏度、室温工作、抗辐照性能和均匀性好等特点,可广泛应用于环境监测、红外遥感、微光夜视、安全检查、激光探测和能源勘探等领
基于延伸波长InGaAs探测器的重要应用,国内外多个团队开展了相关研究。美国普林斯顿红外技术公司研制了截止波长为2 μm的1 280×1 024规模In0.66Ga0.34As探测器,吸收层浓度小于1×1
提升高铟组分InGaAs材料的质量主要从优化缓冲层结构设计和优化生长工艺两方面展开。缓冲层材料有InGaAs、InAlAs、InAsP等多种结
本文利用DCA P600分子束外延系统生长高铟组分InGaAs薄膜,采用双温区源炉作为In和Ga束源炉,采用阀控P裂解炉和阀控As裂解炉分别作为P和As束源炉。为维持组分的一致,在实验之前用束流规对各个源炉的束流进行测试,得到不同束源炉的温度与束流的关系,再通过控制各源炉的温度使得各样品的In组分均为约0.74。将掺Fe的半绝缘InP(100)衬底传送到生长室后升高衬底温度,在300 ℃开P保护,继续升高衬底温度对衬底进行解析,此时反射高能电子衍射图案明显转变为4×2表面再构。在衬底解析完成后将衬底温度降至InP缓冲层的生长温度,然后开始材料生长。

图1 高铟组分InGaAs材料结构示意图
Fig. 1 Schematic structure of high indium InGaAs materials
为优化高铟组分InGaAs材料的分子束外延工艺,生长了多组不同的样品,其生长参数如
样品编号 | In0.74Ga0.26As层生长温度/℃ | V/III比 | As分子束形态 |
---|---|---|---|
A | 550 | 18 | As2 |
B | 570 | 18 | As2 |
C | 580 | 18 | As2 |
D | 590 | 18 | As2 |
E | 570 | 12 | As2 |
F | 570 | 36 | As2 |
G | 570 | 27 | As4&As2 |
H | 570 | 36 | As4 |
采用As2束流,V/III束流比约为18的情况下,对In0.74Ga0.26As外延层的生长温度进行了优化研究,生长了4组样品,样品编号分别为A、B、C和D,其In0.74Ga0.26As层的生长温度分别为550 ℃、570 ℃、580 ℃和590 ℃。
研究了As2束流情况下,As2束流的增加对材料性能的影响。样品E、样品B和样品F,通过增加As炉的阀位,使得As2的束流增加,As/(In+Ga)的束流比(V/III比)相应增加,其V/III比分别为12、18和36。三组样品的In0.74Ga0.26As外延层生长温度均为570 ℃不变。
在分子束外延生长中,V族元素As一般是以As2或As4分子态形式存在的。通过改变As源裂解区的温度,对应不同的As分子形态,当As源裂解区温度为600和1 000 ℃时,As分子的形态分别为As4和As2;当As源裂解区温度为800 ℃时,则包含了As4和As2的混合物。因为不同形态的As分子参与生长和反应的原子数不同,As2分子形态下2个As原子都能参与InGaAs层的生长过程,而As4分子形态下每4个原子只有2个原子参与到InGaAs层的生长过程,另2个原子会脱离开衬底表面而不参与生长过程,所以设计样品B、G和H的V/III比分别为18、27、36,三组样品的In0.74Ga0.26As层生长温度均为570 ℃。
材料生长完成后,用Leica光学显微镜对其表面进行细致观察。基于Nicolet iS50傅里叶变换红外光谱仪对材料进行室温PL测试,采用波长为532 nm的激光对材料进行激发,光谱仪采用液氮制冷InSb探测器对PL进行检测。利用PANalytical X’pert高分辨X射线衍射仪对材料结构特性进行表征。使用HMS-3000霍尔测试仪对材料室温和77 K时的载流子浓度和迁移率进行测试。

图2 样品E的(a)室温PL谱,(b)XRD测试曲线
Fig. 2 (a) PL spectra at RT, and (b) XRD scan curve of sample E
为了更直观地分析PL和XRD随生长温度变化的影响,提取了PL相对强度以及XRD外延峰强度与衬底峰强度之比随In0.74Ga0.26As外延层生长温度的变化,如

图3 (a)PL强度和(b)XRD外延峰半峰宽及XRD外延峰和衬底峰强度之比与生长温度的关系
Fig. 3 (a)PL intensity and (b)XRD FWHM and XRD peak intensity ratio (layer/substrate) as a function of growth temperatures

图4 载流子浓度和迁移率与In0.74Ga0.26As层生长温度的关系
Fig. 4 Background carrier concentration and mobility as a function of growth temperatures of In0.74Ga0.26As layers
样品E、B和F生长时的V/III比不同,但其他生长条件一致。通过对样品进行PL和XRD测试,分析V/III比对高铟组分InGaAs薄膜的影响。PL相对强度以及XRD外延峰强度与衬底峰强度之比随V/III比变化如

图5 (a)PL强度和(b)XRD半峰宽及XRD外延峰和衬底峰强度之比与材料生长V/III比的关系
Fig. 5 (a)PL intensity and (b)XRD FWHM and XRD peak intensity ratio (layer/substrate) as a function of V/III ratios
对不同V/III比的样品E、B和F进行了室温和77 K霍尔测试,载流子浓度和迁移率与V/III束流比的关系如

图6 载流子浓度和迁移率与材料生长V/III比的关系
Fig. 6 Background carrier concentration and mobility as a function of V/III ratios
为了更直观地分析PL和XRD与不同As分子态成分之间的关系,提取了样品H、G和B的PL相对强度以及XRD外延峰强度与衬底峰强度之比,结果如

图7 (a)PL强度和(b)XRD半峰宽及XRD外延峰强度与衬底峰强度之比与As分子形态的关系
Fig. 7 (a)PL intensity and (b)XRD FWHM and XRD peak intensity ratio (layer/substrate) as a function of arsenic dimers

图8 载流子浓度和迁移率与As分子形态的关系
Fig. 8 Background carrier concentration and mobility as a function of arsenic dimers
在文献中对高In组分InGaAs的本底浓度和迁移率报道较少。采用电容-电压测试In0.7Ga0.3As探测器结构吸收层材料的本底浓度低于1E16 c
本文研究了分子束外延生长温度、V/III比以及As分子束形态对高铟组分InGaAs材料光电性能的影响。采用傅里叶光谱仪、高分辨X射线衍射仪和霍尔测试仪对不同工艺下生长的In0.74Ga0.26As材料PL强度、XRD峰强度以及室温和77 K的本底载流子浓度和迁移率进行了测试分析。结果表明,生长温度和V/III束流比适中时,所生长的高铟组分InGaAs薄膜具有较高的PL强度和XRD峰强度以及更优的本底载流子浓度和迁移率。采用As2生长的In0.74Ga0.26As材料质量优于采用As4或As2和As4混合进行生长的材料。通过实验优化,发现在生长温度为570 ℃、采用As2分子束且V/III比为18的条件下生长的In0.74Ga0.26As材料可以实现较高的PL强度和XRD外延峰强度,在室温和77 K下,本底载流子浓度分别达到6.3×1
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