We investigate the photoresponse of mid-wavelength infrared radiation (MWIR) type-II superlattices (T2SLs) InAs/InAsSb high operating temperature (HOT) photoconductor grown on GaAs substrate. The device consists of a 200 periods of active layer grown on GaSb buffer layer. The photoresistor reached a 50% cut-off wavelength of 5 μm and 6 μm at 200 K and 300 K respectively. The time constant of 30 ns is observed at 200 K under 0.5 V bias. This is the first observation of the photoresponse in MWIR T2SLs InAs/InAsSb photocondotocr above 200 K.
Quantum well charge modulation in base region of light-emitting transistors and related electrical-to-optical responses are analyzed by constructing three-port small-signal equivalent circuit models under common-emitter, common-base, and common-collector configurations.
In this paper, we utilize the fin-shaped channel to form the AlGaN/GaN HEMTs which can be considered as “Fin- HEMTs” to adjust the threshold voltage (V<sub>TH</sub>) toward positive value. The gate metal here is deposited directly on the AlGaN/GaN semiconductor to form the Schottky contact. Although the fin-widths are in the level of micron-scale, the shifts of VTH are still observable and the V<sub>TH</sub> becomes more positive with the smaller fin width. This is attributed to the assistant of the side-gate control which can be regarded as the depletion layer formed by Schottky contact at side-gate will deplete the 2DEG in the channel. Therefore, with the smaller fin width, the channel can be pinched off faster which is similar to the double gate MESFETs. The V<sub>TH</sub> of planar device is shifted from -3.81 V to -3.37 V with 2-μm-fin-width. On the other hand, unlike to carrier transportation in the conventional FinFET with nano-scale fin width which is dominated by the surface scattering, our Fin-HEMTs with micron-scale fin width exhibit higher drain current than planar device and this is because of the smaller thermal resistance (R<sub>TH</sub>) for the fin-HEMT. We extract the R<sub>TH</sub> by varying the measured temperature and the R<sub>TH</sub> of the device with 4-μm-fin-width and planar device is 58.5 K/W and 249.5 K/W, respectively.
Possessing both the high-speed characteristics of heterojunction bipolar transistors (HBTs) and enhanced radiative recombination of quantum wells (QWs), the light-emitting transistor (LET) which operates in the regime of spontaneous emissions has achieved up to 4.3 GHz modulation bandwidth. A 40 Gbit/s transmission rate can be even achieved using transistor laser (TL). The transistor laser provides not only the current modulation but also direct voltage-controlled modulation scheme of optical signals via Franz-Keldysh (FK) photon-assisted tunneling effect. In this work, the effect of FK absorption on the voltage modulation of TLs is investigated. In order to analyze the dynamics and optical responses of voltage modulation in TLs, the conventional rate equations relevant to diode lasers (DLs) are first modified to include the FK effect intuitively. The theoretical results of direct-current (DC) and small-signal alternating-current (AC) characteristics of optical responses are both investigated. While the DC characteristics look physical, the intrinsic optical response of TLs under the FK voltage modulation shows an AC enhancement with a 20 dB peak, which however is not observed in experiment. A complete model composed of the intrinsic optical transfer function and an electrical transfer function fed back by optical responses is proposed to explain the behaviors of voltage modulation in TLs. The abnormal AC peak disappears through this optoelectronic feedback. With the electrical response along with FK-included photon-carrier rate equations taken into account, the complete voltage-controlled optical modulation response of TLs is demonstrated.
An integrated on-chip optical device composed of a multiple quantum-well light-emitter and photodetector in the lightemitting transistor (LET) platform is fabricated. The two devices are 400 μm in length and electrically isolated by dry etching with 4.9 μm gap. The two facets are formed by cleaving for optical output. In this report, we discuss the characteristics of the two-section device and demonstrate the optical detection by the heterojunction phototransistor (HPT) under different operation points (I<sub>B</sub> and V<sub>CE</sub>) and injected optical powers. The collector current of the HPT is 74.88 mA without illumination and 83.87 mA under illumination of 7.46μW at V<sub>CE</sub> = 3 V and I<sub>B </sub>= 12 mA, which exhibits 12% increment. The responsivity of the InGaP/GaAs HPT can reach to 711.74 A/W. At the electrical modulation bandwidth of phototransistor fT is enhanced from 1.4 GHz to 1.51 GHz under illumination. This is attributed to the Franz-Keldysh photon-assisted absorption at base-collector junction of light-emitting transistor, which produces additional holes and electrons to enhance the current gain. Through the analysis of small-signal equivalent circuit models, we can show the transit time by de-embedding the circuit parasitic effect. Extracting those parameters can clearly know the thermionic emission lifetime in the quantum well.
The base current (<i>I<sub>B</sub></i>) plays a key role in the transistor since its discovery (16 December 1947, Bardeen and
Brattain). It separates the low impedance input (emitter) from the high impedance output (collector), thus yielding a
“transfer resistor.” Recently, III-V semiconductor material has been fabricated as a heterojunction bipolar transistor
(HBT) which can operate as a high speed device. The HBT can be modified and operated as a three-port light-emitting
device (an electrical input, electrical output, and a third port optical output) by incorporating one or more quantum wells
in the base region, thus becoming a heterojunction bipolar light-emitting transistor (LET). In the present work, we have
designed different sizes of emitter diameter<i> D<sub>E</sub> </i>and base diameter <i>D<sub>B</sub></i> of InGaP/GaAs LETs in aperture layout design.
Through different layout designs, the LETs exhibit different electrical current gain <i>(β= I<sub>C</sub>/I<sub>B</sub>) </i>and optical light output due to different carrier recombination processes in the transistor base region. By reducing the lateral emitter size from 18 to 13 μm, β increases due to the higher injection current densities and better confinement of the radiative recombination in the base region. Moreover, β increases when reducing the base diameter from 27 to 22 μm with fixed emitter diameter. The effective carrier recombination lifetime,<i> τ<sub>rec</sub>, </i>can be estimated from dc analysis and rf measurement (small-signal modulation).We have obtained multi-GHz spontaneous light modulation of LETs, and the device performance is closely related to different layout designs with different device parasitics.