H. Namizaki

Transverse‐junction‐stripe‐geometry double‐heterostructure lasers with very low threshold current

A new geometry DH laser is developed in which a very thin GaAs homojunction laser is sandwiched by (GaAl)As layers. The minimum threshold current is 63 and 80 mA for pulsed and cw operation at room temperature, respectively. The possibility of further reduction of threshold current is briefly mentioned.

Current dependence of spontaneous carrier lifetimes in GaAs–Ga1‐xAlx As double‐heterostructure lasers

The spontaneous lifetime of injected carriers in GaAs–Ga1‐xAlx As double‐heterostructure lasers is examined in relation to the current injection levels. It is shown that the spontaneous lifetime at threshold is proportional to Jth−1/2 in lasers with a 2×1017/cm3 Si‐doped active region. From the proportionality constant the effective recombination constant Beff is estimated to be 9.0×10−11 cm3/sec, which agrees quite well with the theoretical value for band‐to‐band transitions.

High temperature single‐mode cw operation with a junction‐up TJS laser

A modified TJS laser has been developed, in which the current is effectively confined to the active region. When heat sinked through the substrate, the laser operates continuously at over 100 °C in a single longitudinal and fundamental transverse mode.

Low threshold InGaAsP/InP buried crescent laser with double current confinement structure

An InGaAsP/InP laser diode emitting at 1.3 μm with a crescent shaped active region is described. The active region is completely embedded in InP by a two-step LPE technique, and a double current confinement scheme is incorporated with two reverse biased p-n junctions at both sides of the active layer. A threshold current as low as 20 mA has been achieved in CW operation at room temperature. Fundamental transverse mode operation with linear light output-current characteristics and single longitudinal mode oscillation have been obtained.

High-power 1.3-µm InGaAsP P-substrate buried crescent lasers

High performance of newly developed InGaAsP P-substrate buried crescent (PBC) laser diodes is described. It is shown that the PBC laser has superior characteristics to the conventional buried crescent (BC) laser with n-InP substrate. The maximum output power of 140 mW under a CW condition is realized at room temperature. CW light output power of 10 mW up to 110°C is achieved. A maximum CW temperature of 135°C is obtained. Stable CW operations have been confirmed in 70°C 5-mW and 70°C 20-mW aging tests. The reason for the high performance is discussed in relation to the leakage current which flows through the current blocking layers.

InGaAsP/InP buried crescent laser diode emitting at 1.3 µm wavelength

The fabrication procedure, designing of an active region and a p-n-p-n current blocking structure, characteristics and the aging results of an InGaAsP/InP buried crescent (BC) laser diode are described. The BC laser diodes exhibit high laser performances, such as a low-threshold current, a fundamental transverse mode oscillation with linear light output-current characteristics. CW operation at as high as 100°C is achieved with a junction up configuration as a result of the improvement in the current blocking structure. A stable CW operation at 80°C has been realized with a constant optical output power of 5 mW.

Hydrogen passivation of polysilicon thin film transistors by electron cyclotron resonance plasma

We have investigated the method of hydrogenation of polysilicon thin-film transistors (TFT) by electron cyclotron resonance (ECR) plasma. It is found that with decreasing pressure (1.5 to 0.35 mTorr) of the hydrogen plasma, the substrate temperature rises due to bombardment of hydrogen ions. At the same time, the amount of hydrogen supplied by the ECR plasma increases. Due to these two effects, the passivation proceeds more quickly under low pressure. The amount of hydrogen supplied by a low-pressure ECR hydrogen plasma is higher than that supplied by other means such as Al sintering or rf hydrogen plasma. When polysilicon TFTs are exposed to the ECR hydrogen plasma, the hydrogenation reduces 75% of the electrically active defect states in 15 min. Polysilicon TFTs with an offset-drain structure reached an on/off current ratio of 8 decades after such ECR hydrogen passivation.

Dark current and diffusion length in InGaAs photodiodes grown on GaAs substrates

In0.53Ga0.47As photodiodes grown on GaAs substrates have been fabricated and analyzed. The dislocation density in the InGaAs layer is 2×107 cm−2. A lowest dark current of 3.8×10−4 A/cm2 at 10 V bias is obtained, which is very stable during a bias‐temperature test of Vb=−10 V, T=175 °C, and t=100 h. The quantum efficiency is more than 85% at λ=1.3 μm. This device is expected to be practically used. The dark current has been successfully explained by the thermionic emission and thermionic field emission from traps at midgap. The diffusion length of holes in the InGaAs layer is explained by the recombination at dislocations with the finite recombination velocity of S∼104 cm/s.

Position of the degradation and the improved structure for the buried crescent InGaAsP/InP (1.3 μm) lasers

We have found a degradation of the buried crescent (BC) InGaAsP/InP lasers that occurs when the p‐n junction plane coincides with the surface exposed in the high‐temperature H2 ambient before the melt contact during the liquid phase epitaxial growth. To eliminate the degradation, we have fabricated a new structure of the BC laser and have obtained stable cw operation at 80 °C.

Ten-thousand-hour operation of crank transverse-junction-stripe lasers grown by metal-organic chemical vapor deposition

For over 10 000 h, crank transverse-junction-stripe (TJS) laser diodes, grown by metal-organic chemical vapor deposition (MOCVD) maintain low and quite stable operating currents in the automatic-power-control aging with output power of 5 mW/facet at 55°C and 70°C. These MO-CVD lasers have excellent initial characteristics and small distributions of the characteristics. The reason for this excellent result is discussed in relation to the crystalline quality and the uniform growth of MO-CVD wafers.