Nobuyuki Otsuka

A DC-isolated gate drive IC with drive-by-microwave technology for power switching devices

Outstanding GaN-based HFETs (HFET: Heterojunction Field-Effect Transistors) [1] power devices are expected to replace all Si power devices in high power applications such as inverter systems due to their excellent performance. In order to exploit the full potential of such emerging GaN power devices, the gate driver that controls the device by a pulse width modulation (PWM) signal is becoming more important. The vital function of the gate driver is to provide an isolated gate signal against the reference source voltage that operates at high voltage. In addition to this function, their integration with GaN power HFETs is also desirable to achieve smaller system size, lower cost and user-friendliness. Although there are several signal isolation techniques for a gate driver such as to use a photo-coupler and wireless pulse transformer [2], these techniques have disadvantages such as large system size and difficulty in integration. Other bootstrap or charge pump techniques [3] in high voltage gate drivers (HVIC) have been developed to generate a reference voltage, but the driver can only be used in particular applications such as inverters. Meanwhile, we have focused our attention on the recent technology of wireless power transmission using an electromagnetic resonant coupler (EMRC) [4] with an open-ring resonator [5], which is very attractive due to its high efficiency in power transmission and its compactness at high frequency.

Room Temperature 339 nm Emission from Al0.13Ga0.87N/Al0.10Ga0.90N Double Heterostructure Light-Emitting Diode on Sapphire Substrate

Room-temperature deep-ultraviolet emission has been observed from Al0.13Ga0.87N/Al0.10Ga0.90N double heterostructure light-emitting diodes (LEDs) on (0001)-oriented sapphire substrate. By introducing undoped barrier layers, which sandwich the active layer, the LED was operated at a peak emission wavelength of 339 nm with a narrow linewidth of 5.6 nm. The dependence of emission intensity on injection current suggests that the nonradiative recombination was suppressed and the diffusion current for the recombination process was dominant at the injection current of over 20 mA.

A one-chip isolated gate driver with an electromagnetic resonant coupler using a SPDT switch

The isolated direct gate driver with Drive-by-Microwave technologies can directly drive a power switching device by wireless power transmission of RF modulated signal through the electromagnetic resonant coupler and requires no additional isolated voltage source. In order to improve the performance such as a fall time characteristic and a power consumption of the gate driver, a new direct gate driver using a SPDT switch is proposed, which can effectively switch the inter-channels for the positive and negative voltage outputs. The fabricated GaN single-chip direct gate driver realized 2.0Mbps signal isolation and successfully drove a GaN power switching device with a very fast fall time by the negative voltage output for off-state.

High-power, wide-temperature range operation of 1.3-μm gain-coupled DFB lasers with automatically buried InAsP absorptive grating

DFB lasers operating at 1.3 /spl mu/m with gain-coupling structure show single-mode operation over a wide temperature range of -20/spl sim/85/spl deg/C and up to a high power of 130 mW. These lasers have InAsP absorptive grating, which can be formed by a substantially simplified fabrication process, involving annealing a corrugated InP substrate in an atmosphere of mixed arsine and phosphine.

Enhanced relaxation oscillation frequency of 1.3 /spl mu/m strained-layer multiquantum well lasers

Dependence of relaxation oscillation frequency (f/sub r/) on the bandgap wavelength of InGaAsP barrier layers (/spl lambda//sub g//sup b/) and number of quantum wells (N/sub w/) were investigated for the first time, for 1.3 /spl mu/m InGaAsP/InGaAsP compressively strained multiquantum well (MQW) lasers. 1.3 times higher f/sub r/ was confirmed for strained-layer MQW lasers with large N/sub w/ (N/sub w//spl ges/7) and wide bandgap barrier layers (/spl lambda//sub g//sup b/=1.05 /spl mu/m) at the same injection level, compared with unstrained MQW lasers having the same well thicknesses and the same emitting wavelength. This enhancement mainly results from increased differential gain due to strain effects separated from the quantum-size effect.<<ETX>>

Control of double diffusion front unintentionally penetrated from a Zn doped InP layer during metalorganic vapor phase epitaxy

Unintentional Zn diffusion during metalorganic vapor phase epitaxy causes serious damages in semiconductor devices. In this work, profiles of unintentionally diffused Zn atoms from a p-InP layer to the adjoining InP substrate during growth of the p-InP layer are measured by secondary ion mass spectrometry. Zn diffusion profiles with a double diffusion front, which is composed of a shallow front with high Zn concentration and a deep front with low Zn concentration, are investigated as an approach to controlling unintentional diffusion. Diffusion depth of each front is controlled in proportion to Zn dosage, which is proposed as a value calculated as Zn concentration without regard to saturation limit. The diffusion depth for the growth time of 60 min increases in proportion to the Zn dosage as the slope of 0.16 μm/1018 cm−3 for the shallow front and that of 0.32 μm/1018 cm−3 for the deep front at a growth temperature of 600 °C. The deep front expands two times faster than the shallow front, which is normall...

Stability of Zn doping profile in modulation‐doped multiple quantum well structure

Stability of the Zn doping profile in InGaAs/InGaAsP modulation‐doped multiple quantum well (MD‐MQW) structures grown by low‐pressure metalorganic vapor‐phase epitaxy (MOVPE) has been investigated by secondary ion mass spectrometry and transmission electron microscope with wedge‐shaped samples. Although excellent stability of Zn profile is confirmed in an as‐grown sample with modulation doping (d=3 nm CZn=1×1018 cm−3), the modulation‐doping structure diminishes after the second epitaxial regrowth of a p‐InP layer (CZn=1×1018 cm−3) carried out by either liquid phase epitaxy or MOVPE, which is applicable for buried heterostructure lasers. However, the modulation‐doping profile is successfully preserved even after regrowth of the p‐InP layer for 90 min in a sample constructed of an undoped InP clad layer instead of a p‐InP clad layer superposed on the MD‐MQW layers. A Zn diffusion coefficient in the modulation‐doped region is extremely small, having a value of less than 7×10−18 cm2/s. The maximum Zn concentr...

New structure by selective regrowth in multi-quantum well laser diodes performed by low pressure metalorganic vapor phase epitaxy

Abstract InGaAsP/InP multi-quantum well (MQW) planar buried hetero-structure (PBH) lasers which are grown entirely by metalorganic vapor phase epitaxy (MOVPE) on n-InP substrates are demonstrated. Two types of lasers, which are different in ridge shape (reentrant or non-reentrant), are investigated in respect of regrowth structure and damage at the regrowth interface. A new regrown structure constructed of a uniformly thick n-InP current-blocking layer formed on a reentrant ridge stripe is demonstrated for the first time. This structure is expected to be effective to suppress leakage current in laser operation. Furthermore, it is found that threshold current and reliability are strongly dependent on regrowth conditions. High quality regrowth interfaces are realized by optimizing regrowth thermal procedure and hole concentration of p-InP current-blocking layer. Stable laser characteristics in accelerated aging tests have been confirmed in both types of lasers.

A Drive-by-Microwave isolated gate driver with a high-speed voltage monitoring

A new isolated Drive-by-Microwave (DBM) gate driver with a high-speed voltage monitoring for over current detection is proposed, which is composed of a 2.4GHz GaN/Si DBM transmitter, DBM receiver chip and compact isolated couplers in a low-cost printed circuit board. The fabricated DBM gate driver demonstrates a 200 Mbps isolated data transmission and a GaN power switching devices driving with a turn-on skew rate of 4.2kV/us. Furthermore, it successfully detects the isolated 1.0Mbps monitoring signal at the secondary side without any isolated voltage source by means of detecting the 2.4GHz return power changing that results from the impedance miss matching of the varicap diode at a receiver.

SELF-LIMITING GROWTH CONDITIONS ON (001) INP BY ALTERNATE TRIETHYLINDIUM AND TERTIARYBUTYLPHOSPHINE SUPPLY IN ULTRAHIGH VACUUM

Alternate injections of triethylindium (TEI) and tertiarybutylphosphine (TBP) without precracking were used to realize self-limiting growth of an InP layer on a (001) InP substrate in ultrahigh vacuum. Self-limiting growth, in which the growth rate is independent of the injection time and the pressure of TEI and TBP, was achieved at a growth temperature as low as 320 °C. The growth rate of around 0.75 ML per cycle in self-limiting growth was assumed to be due to stable surface reconstruction of (2×4)-β. A specular surface morphology was obtained in the self-limiting growth condition. By analyzing the limitation of the growth rate as well as the surface morphology of the layer, self-limiting mechanisms were proposed with respect to suppression of the TEI decomposition on the indium surface during TEI injection, suppression of the phosphorus dissociation from the InP surface during TBP evacuation, and complete reaction between TEI and TBP during TBP injection. The growth condition range for self-limiting gr...