双异质结单载流子传输光敏晶体管输出电流

Output current of double heterojunction uni-travelling-carrier phototransistor

详细对比并分析了双异质结单载流子传输光敏晶体管(Uni-travelling-carrier Double Heterojunction Phototransistor,UTC-DHPT)与单异质结光敏晶体管(Single Heterojunction Phototransistor,SHPT)在大的入射光功率范围下集电极输出电流特性.首先,UTC-DHPT仅选取窄带隙重掺杂的基区作为吸收区,与SHPT选取基区和集电区作为吸收区相比,其光吸收区厚度小,在小功率入射光下UTC-DHPT的输出电流小于SHPT的输出电流.其次,由于UTCDHPT的双异质结结构,光生电子和光生空穴产生于基区,减弱了SHPT因光生空穴在集电结界面积累而产生的空间电荷效应,避免了SHPT在小功率入射光下输出电流开始饱和的问题,从而UTC-DHPT获得了比SHPT更大的准线性工作范围.最后,UTC-DHPT的单载流子(电子)传输方式使得基区产生的光生空穴以介电弛豫的方式到达发射结界面,有效降低了发射结势垒,增加了单位时间内由发射区传输到基区的电子数量,提高了其发射结注入效率,在大功率入射光下UTC-DHPT比SHPT能获得更高的输出电流.

In this paper,the output current characteristics within a large range of incident light power of a double heterojunction uni-travelling-carrier phototransistor（ UTC-DHPT） were analyzed in detail and compared with a single heterojunction phototransistor（ SHPT） simultaneously. Firstly,the output current of UTC-DHPT is smaller than that of SHPT under small power incident light because the UTC-DHPT ＇s absorption section is only the base region,which is smaller than SHPT ＇s absorption section consisting of base and collector. Secondly,benefiting from the double hetero-junction,the photogenerated carriers are only generated in base in UTC-DHPT,and there are fewphotogenerated holes accumulated in the collector junction interface. The space charge effect,which is seriously in SHPT,is effectively alleviated. Furthermore,the saturation of the output current under small power incident light,which always occurs in SHPT,is avoided. Therefore,UTC-DHPT has a larger quasi linear range than SHPT. Lastly,the uni-travelling transportation in UTC-DHPT make photogenerated holes in the base region reach to the emitter junction interface by the rapid relaxation,and thereby effectively reduce the emitter junction barrier. This would increase the number of electrons transmitting from the emitter to the base in the unit-time,and the emitter junction injection efficiency is improved. Thus,UTC-DHPT can obtain higher output current than SHPT under the high power incident light.