Research On InP Double Heterojunction Transistor Photoelectric Devices

Optoelectronic integrated circuit (OEIC) is one of the technologies currentlysupporting high-speed and large-capacity integrated services data network. Low costOEIC chip becomes an important research focus. Transistor photoelectric device,which combines advantages of electric transistors and characteristics of semiconductoroptical devices, greatly increases the likelihood of implementation of high integrationand low cost OEIC chip. Thus the transistor photoelectric device has attracted muchattention. Transistor photoelectric devices include heterojunction phototransistors(HPT), transistor lasers (TLs) and light emitting transistor (LETs). The advantages ofphototransistors include large optical gain, high frequency response, low noise, highresponsivity and easy integration with heterojunction bipolar transistor (HBT). Theadvantages of TLs and LETs contain double controlled mode of operation, large directmodulation bandwidth and good nonlinear effect. With the development of opticalcommunication network, the transistor photoelectric devices are widely concerned andresearched due to their excellent characteristics.There is a contradiction between detection efficiency and working speed intraditional signal heterojunction HPT, although it has many merits. In order to ease thecontradiction and achieve both high responsivity and high characteristic frequencysimultaneously, the idea of uni-traveling-carrier (UTC) was used in the doubleheterojunction phototransistor forming the uni-traveling-carrier double heterojunctionphototransistor (UTC-DHPT). Its basic performance and the effects of structureparameters on the device performance have been simulated and analyzed. A betterstructure of the UTC-DHPT has been proposed to achieved both high responsivity andhigh characteristic frequency simultaneously. For UTC-DHPT, the main work is asfollows:Firstly, a two-dimensional (2D) model of UTC-DHPT was established. The basicperformance of the UTC-DHPT, such as responsivity and characteristic frequency,output characteristics are studied in detail. The results shows: the responsivity is17.6A/W, considerably larger than the PIN’s and APD’s; its characteristic frequency is115.4GHz, larger than the common HPT’s; output character is similar with a commonheterojunction bipolar transistor (HBT).Secondly, the effects of structure parameters on responsivity and characteristic frequency of the UTC-DHPT were analyzed. The relationship between UTC-DHPTresponsivity and the responsivity of corresponding PIN, current gain (β) ofcorresponding HBT was analyzed too. The results have shown that the responsivity ofUTC-DHPT is closed to the product of the PIN’s responsivity and the β of DHBT.Thirdly, an optimized UTC-DHPT with optimized structure parameters, especiallythe parameters of the transition layer between base and collector, was fabricated andtested. The results show that responsivity of the UTC-DHPT is15.5A/W, which isenough to show UTC-DHPT advantage in terms of responsiveness.InP light-emitting transistors (LETs) and transistor lasers (TLs) have manyadvantages and they are more suitable for optical fiber communication than GaAs TLs.But InP npn HBTLs just work below-40oC, So it become very necessary to improve itsworking temperature. Besides, the working principle of InP npn LET and to improveits performance need to be further studied. For TLs and LETs, the main work is asfollows:Firstly, shallow ridge and deep ridge TLs and LETs were compared and analyzed.The results show that light output power of deep ridge LELs is slight lower than that ofthe shallow ridge LETs and the deep ridge HBTLs is easier working at roomtemperature. Then the deep ridge LETs and HBTLs were fabricated and tested indetails.Secondly, part of test results of LET show as VCEis increased, the output powerincreases with the base current with a larger slope efficiency and the slope efficiencydecreases when the base current exceeds a certain value. Both the current at which thesaturation starts and the saturation power increase with VCE,which are agree with thenumerical study of Shi. Furthermore, the results have shown what unique to the LETs isthat under the collector bias voltage of1.6V and1.8V, the trend of decrease of the lightpower slows down after the base currents are larger than about65mA and75mA. Also,the performance of LET with different cavity length and different working temperatureare analyzed through multiple measurments.Thirdly, light output power and threshold current of the HBTL at differenttemperature were tested, the results show that laser operation at near room temperatureis achieved in the deep ridge LET with800μm, with a~1.5μm emission wavelength.The calculated characteristic temperature of the device is31K, which is typical for anInP based laser.